Most parish priests like to be able to draw on the help of between one and six altar servers at any one time. Traditionally, the lay ministry of altar servers was open only to males, and particularly boys, in the expectation that their experience of the liturgy might inspire a vocation to the priesthood among some of them. Since 1992, however, girls have also been permitted to serve at the altar, if they are allowed to by the diocesan bishop and wished for by the priest.

There is no age restriction for an altar server and some adults continue in the ministry well into old age. It is, however, the norm to draw altar servers from children who are practising Catholics and who have made their First Holy Communion.