High School Years Question

I have had High School Years for a few months, and I noticed something odd today. My Sim got invited to graduation (from attending a few of the sports events, he did know a few of the high schooler Sims). My Sim has always been a Young Adult, and for the past several saves, he's had a few college degrees under his belt. Yet, he showed up in a cap and gown.

I noticed that all the formerly teenage Sims had aged up to young adults as well. Aging is completely turned off in my game.

Is this normal?