Upvote:4
The Aaronic Priesthood is the preparatory priesthood--boys growing up in The Church of Jesus Christ of Latter-day Saints will generally progress through the offices of deacon, teacher, and priest in the Aaronic Priesthood over the course of 6-7 years.
For new converts who will be 16 (or older) by the end of the year they join the church, they can be ordained to the office of priest (no requirement to officiate as a deacon or teacher first); there is no set time requirement for how long after baptism & confirmation conferral of the Aaronic Priesthood can occur, but the church handbook recommends the Bishop interview him for ordination within a week.
In the past, it was common to wait until a year after baptism for a new, adult member of the church to be eligible to receive the temple endowment. Since men must hold the Melchizedek Priesthood in order to be endowed in the temple, the 1-year milestone served as the timeline for helping a convert prepare for and receive the Melchizedek Priesthood, prepare for the temple, and receive the endowment.
Recent policy changes have established the following guidelines for a new member to receive the Melchizedek Priesthood:
A new member is eligible to receive the Melchizedek Priesthood and be ordained an elder when he:
Is 18 or older.
Has served as a priest (no specified time is required).
Has sufficient understanding of the gospel.
Has demonstrated worthiness.
Policies taken from General Handbook: Serving in The Church of Jesus Christ of Latter-day Saints 38.2.9.1