What is the Catholic understanding of 'age' in Scripture and in its Tradition?

The word "saeculum" is the Latin word used for "age" in many Catholic writings, and in the Scripture passages that you mention in your question. This word is defined as "a generation; the spirit of the age , the times; a hundred years, a century, an age" by this Latin dictionary.

According to etymonline.com (and others), the English word "secular" derives from the Latin word "saeculum" by an interesting path. "Saecularis" is a Latin adjective that means "pretaining to an age." This contrast was used by medieval writers to refer to the present age, or to the general doings of the world, and from this distinction arises the modern sense of "secular" meaning "non-religious." (Also, the "secular priesthood," is the body priests who live in the world, as opposed to in monasteries, that is, to diocesan rather than order priests.) The sense of "age" (= "saeculum") referring to the present world, or the present created order (that is, the world before the Last Day), is contrasted with the "age to come" (Latin "venturum saeculum") as in the Latin Nicene creed, "vitam venturi saeculi," which means, "the life of the world to come" or "life of the age to come."

The quotation from Matthew 12 and from Mark 10 use "age" in this sense, to contrast the present order of creation with that which will exist after Christ comes again.

The quotation from 1 Corinthians shows us a slightly different sense. In ancient culture, there was a sense of repetition or succession of ages ("saecula", plural). Paul is alluding to the fact that the ages will no longer succeed one after another, but rather once Christ has returned all things will be completed, and the transient succession of "saecula" will end. (In some cases, a "saeculum" is the duration of a particular political arrangement, and in some cases it is a period of 100 years. The Romans celebrated "Ludi saeculares" roughly every 100 years, though Augustus Caesar caused them to be celebrated so that they might mark his inauguration of a new period of Roman government and show a continuation of an ancient tradition.)

The quotation from Ephesians shows that the name of Jesus is supreme, both in the current, transient created order and in the "age to come," that is, in the perfected order that will arise after Christ returns. This sense, the contrast of "now" against "after Second Coming," is the same sense as found in your quotations from the Evangelists.

As an aside, I would also note that although it is not reflected in the English translation, "Glory to the Father, to the Son, and to the Holy Spirit, as it was in the beginning, is now, and will be forever, world without end," the use of "saeculum" occurs in the Latin version of this prayer, where we see "et in saecula saeculorum," literally, "into the ages of ages," rather than "world without end." A similar expression of "into the age of an age" or "into the ages of ages" is found in the doxology in many Psalms, and in the hymn of Daniel and his companions in the furnace.

Regarding the Nicene Creed, the phrase "born of the Father before all ages," (Latin: "ex Patre natum ante omnia saecula") indicates that Christ's existence precedes the existence of every successive period of creation, including this present age (Latin "hoc saeculum"). This is the same sense of "saecula" (plural) found in 1 Corinthians as discussed above.

In summary, there are two related senses of "age" in this tradition. "This age" or "the present age" (usually singular, Latin "hoc saeculum") contrasted with the "age to come," (Latin "saeculum venturum"), and meaning simply the current order of creation before Christ returns. The second sense, "ages," usually plural, refers to successive periods of creation, usually looking at times past before the author wrote, as when Paul speaks of the "end of the ages" meaning roughly "the cessation of the quasi-cyclical rise and fall of nations, passage of seasons, etc., and their replacement with whatever God has prepared in the age to come."

I don't know enough to comment on the numerical interpretation of Revelation. I hesitate to point to any literal correspondence between the Revelation of St. John and real world events, historical or predicted, but that is only my opinion, and is really a caution born of ignorance.

You may be right that the change from "from age to age" to "you never cease" is meant to avoid accidentally using this sense of age. Another goal of the recent translation was to follow the Latin more closely, and the Latin in this case reads simply "et populum tibi congregare non desinis" literally "you do not cease to gather a people for yourself."

I hope I've answered your question adequately. I answer from the perspective of what the word "age" in Latin means, and, as a Latin teacher, I am much more confident of the Latin than of any theological implications I may accidentally have made.