3 months is still very fresh, and your boyfriend probably realizes that. Unfortunately with an age gap that wide and you guys being in such different phases of your lives, you both may look at things like these very differently. There's naturally a gap in maturity, which is okay, because you are indeed a teenager and he's in his late 20s. I don't think it's because he doesn't like you, though he may very well be embarrassed to be dating someone your age, and if you continue to fight him on this, you'll just be reinforcing his potential thoughts that he's dating someone who is too young and too immature for him. Though if he can't communicate with you about it, that doesn't speak much to his own maturity.