Does the Pope Francis' moto proprio Spiritus Domini mean that pastors cannot limit servers to only boys?

Does the Pope Francis' Motu Proprio Spiritus Domini mean that pastors cannot limit servers to only young men?

Yes

That seems to be the gist of the document, but episcopal conferences will make their own legislative decisions on this matter.

This question concerns the Ordinary Form of the Mass only. If Pope Francis removed the word "vir" (man) from the code of canon law, them it means women can be acolytes and lectors. We can all see where this is going....

Girls have been allowed to be servers at the altar for a number of years already.

Pope Francis’ document, I believe elevates the possibility of women becoming officially instituted as acolytes and/or as instituted lectors by the local ordinaries (bishop). It is unclear if his intention is for permanent offices or simply on a yearly bases. Whether it is for one parish or the entire diocese.

Up until the 1990s girls did not serve at Mass. They have never been permitted in the Extraordinary Form of the Mass. The Extraordinary Form of the Mass has retained it traditional norms governing the sacraments. Female servers are not permitted.

The Holy See provided two clarifications in the 1990s. On 30 June 1992, the Pontifical Council for the Interpretation of Legislative Texts issued an authentic interpretation of that canon declaring that service at the altar is one of the "other functions" open to lay persons in general.[16] On 15 March 1994, the Congregation for Divine Worship affirmed that both men and women may serve at the altar, that each bishop has the discretion to determine who may serve, and that "it will always be very appropriate to follow the noble tradition of having boys serve at the altar".

On 10 January 2021, Pope Francis ordered a modification to canon law and related norms to state explicitly that all baptized persons can be admitted to the instituted ministries of lector and acolyte. Where women and girls already had the ability to exercise these functions "by temporary designation", he indicated their eligibility for these roles "on a stable basis". - Female altar servers

Seminarians are generally instituted lectors and then acolytes for about a year as a steppingstone towards priestly ordination! Doubt this will change.

Accepting these recommendations, a doctrinal development has taken place in recent years which has highlighted how certain ministries instituted by the Church are based on the common condition of being baptised and the regal priesthood received in the Sacrament of Baptism; they are essentially distinct from the ordained ministry received in the Sacrament of Orders. A consolidated practice in the Latin Church has also confirmed, in fact, that these lay ministries, since they are based on the Sacrament of Baptism, may be entrusted to all suitable faithful, whether male or female, in accordance with what is already implicitly provided for by Canon 230 § 2.

Consequently, after having heard the opinion of the competent Dicasteries, I have decided to modify canon 230 § 1 of the Code of Canon Law. I therefore decree that canon 230 § 1 of the Code of Canon Law shall in future have the following wording:

“Lay persons of suitable age and with the gifts determined by decree of the Episcopal Conference may be permanently assigned, by means of the established liturgical rite, to the ministries of lectors and acolytes; however, the conferment of such a role does not entitle them to support or remuneration from the Church”. - APOSTOLIC LETTER ISSUED "MOTU PROPRIO" SPIRITUS DOMINI ((10 January 2021)

Generally speaking MC’s are priests, when the bishop is present at the cathedral! For the rest anyone’s guess is good.

The Master of Ceremonies is not necessarily a lector or an acolyte. They are distinct roles.

The Master of Ceremonies in parishes is technically not a Master of Ceremonies. They are called such in general terms, but in actuality they are not. In general, the MC may correct any person involved in the execution of a liturgical rite, including the celebrant himself. This is not done at the parish level by a so called MC.

Master of ceremonies

Definition

A male cleric who supervises and directs the proceedings in any formal observance of a religious rite. He has complete authority within the limits of his office, especially guiding the actions of the celebrant and his assistants according to the rubrics of the Sacred Liturgy. In general the person who directs the proceedings of any observance where specific procedure is required.

What is an instituted acolyte?

Acolyte

Definition

A ministry to which a person is specially appointed by the Church to assist the deacon and to minister to the priest. His duty is to attend to the service of the altar and to assist as needed in the celebration of the Mass. He may also distribute Holy Communion as an auxiliary minister at the Eucharistic liturgy and to the sick. An acolyte may be entrusted with publicly exposing the Blessed Sacrament for adoration but not with giving benediction. He may also, to the extent needed, take care of instructing other faithful who by appointment assist the priest or deacon by carrying the missal, cross, candles, and similar functions. The ministry of acolyte is reserved to men and conferred by the bishop of the diocese or, in clerical institutes of religious, by the major superior, according to liturgical rites composed for the purpose by the Church. Women may be delegated to perform some of the functions of an acolyte.

What is an instituted Lector?

Lector

Definition

One of the ministries adapted to present day needs in the Latin Church, otherwise known as reader. He functions partially as the subdeacon did previously. He is appointed to read the word of God in the liturgical assembly. Accordingly he reads the lesson from Sacred Scripture, except the Gospel, in the Mass and in other sacred celebrations; recites the psalms between the readings in absence of the psalmist; presents the intentions for general intercessions when the deacon or cantor is absent; and may also direct the congregation in the singing. If necessary he also assumes the responsibility of instructing any of the faithful called upon to read the Scriptures in any liturgical celebration.

The 1983 code can. 230 §1 was:

Lay men (viri laici) who possess the age and qualifications established by decree of the conference of bishops can be admitted on a stable basis through the prescribed liiturgical rite to the ministries of lector and acolyte. Nevertheless, the conferral of these ministries does not grant them the right to obtain support or remuneration from the Church.

The motu proprio removed "viri":

Lay persons (laici) who possess the age and qualifications established by decree of the conference of bishops can be admitted on a stable basis through the prescribed liturgical rite to the ministries of lector and acolyte. Nevertheless, the conferral of these ministries does not grant them the right to obtain support or remuneration from the Church

This cannot introduce girl altar servers into the "Extraordinary Form" (1962 or earlier usages), according to Universæ Ecclesiæ (30 April, 2011), "Liturgical and Ecclesiastical Discipline":

28. Furthermore, by virtue of its character of special law, within its own area, the Motu Proprio Summorum Pontificum derogates from those provisions of law, connected with the sacred Rites, promulgated from 1962 onwards and incompatible with the rubrics of the liturgical books in effect in 1962.

Girl altar servers are "incompatible with the rubrics of the liturgical books in effect in 1962".