In many parishes, choirs sing, but parishioners don’t — no matter their age. Host a parish music night when the choir director talks to your young adult group and teaches them some of the hymns most often sung at mass. Learning hymns in a smaller group will make them seem less ancient to young adults and will get them more involved in the mass, hopefully spur the other congregants to sing. If there is sufficient interest, talk to the music director about possibly forming a young adult choir. Encourage not only singers, but instrumentalists to join — since only hearing the organ week after week can get boring, adding in a guitarist or drummer could be a breath of fresh air.