Young men are encouraged to serve missions when they turn 19. Young women have the opportunity to serve when they turn 21. Young men and women must be unmarried to serve a mission, but retired couples can serve missions together, as long as health permits. These retired couples can serve several missions.
Missionaries often speak to the congregation during Sacrament Meeting when they depart on their missions, and when they return home. This is meant to be a single talk, according to Church policy. However, tradition often got out of hand. Sacrament meetings in which missionaries spoke were called "farewells" and "homecomings," and the missionary and his or her family, instead of the bishop, would often end up running the program, especially in the case of "farewells." Every member of the family would often speak, and there would be special musical numbers.
Another traditional aspect of the "farewell" was an "open house" after the meeting, in which the family of the missionary would often open up their home to many guests.
In the October General Conference of 2002, President Gordon B. Hinckley presented a modification of this tradition. In some wards, "farewells" and "homecomings" ended up taking over far too many sacrament meetings. He stated that while missionary work is very important, no other call in the Church gets nearly so much celebration and that missionary service is a reward in itself. The missionary may speak in the congregation when they leave and when they return, but their families should not speak in the same meeting and there should be no special musical numbers. Nor should there be massive open houses after sacrament meeting, although family gatherings are fine.