Canon 230 governs the installed acolytes, which is an instituted role open to adult lay men with qualifications established by the bishop’s conference.
When there are no instituted acolytes, lay persons may fulfill these roles. There are no qualifications per canon law. In practice, altar servers must have at least received First Communion, so 7 or 8 years old. There is no upward “age limit” as adult servers are common.
Your boys are simply at “that age” where Church is not cool.
Can. 230 §1. Lay men 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.
§2. Lay persons can fulfill the function of lector in liturgical actions by temporary designation. All lay persons can also perform the functions of commentator or cantor, or other functions, according to the norm of law.
§3. When the need of the Church warrants it and ministers are lacking, lay persons, even if they are not lectors or acolytes, can also supply certain of their duties, namely, to exercise the ministry of the word, to preside offer liturgical prayers, to confer baptism, and to distribute Holy Communion, according to the prescripts of the law.