I made a teen in CAS and now she is approaching YA. She got straight A's lvl 3 in her career and is in range for the responsible trait. She also got a boyfriend that their made promises to each other...
If he doesn't age up before your sim (depends on your gameplay settings if you've set townies to age) you can always invite him to the party, put a pair of birthday candles on a cake and let him blow out the candles. There's a special interaction on it that allows you to age up whomever is around that you know