Church documents certainly allow men to the be altar servers. Generally the preference seems to be for men, instituted acolytes, but also encouraging boys.
Only men can be instituted acolytes, not women. According to the Motu Proprio of 1972 “Ministeria Quaedam” by Pope Paul VI:
“7. In accordance with the ancient tradition of the Church, institution to the ministries of reader and acolyte is reserved to men.” (From Documents on the Liturgy 1963-1979, Liturgical Press, Minnesota, 1982, pages 908-911).
And in 8b it requires: “a suitable age and special qualities to be determined by the conference of bishops;”.
So a country’s Conference of Bishops will determine the exact age, but there is an indication that it is for men, not boys.
In the 2002 General Instruction of the Roman Missal (GIRM):
“100. In the absence of an instituted acolyte, lay ministers may be deputed to serve at the altar and assist the priest and the deacon; they may carry the cross, the candles, the thurible, the bread, the wine, and the water, and they may also be deputed to distribute Holy Communion as extraordinary ministers.”
This seems to be saying do not use altar boys if you have instituted acolytes.
But in the 2004 Instruction “Redemptionis Sacramentum” we are told:
“[47.] It is altogether laudable to maintain the noble custom by which boys or youths, customarily termed servers, provide service of the altar after the manner of acolytes, and receive catechesis regarding their function in accordance with their power of comprehension.”
My opinion is that there should be clearer encouragement to use adult altar servers, rather than children.