Make sure you have an ID with you always. You're right, people can't judge ages accurately (hurrah alcohol checks) and a tall guy can often be perceived as older. Where as short or chubby is often more associated with young. That has nothing to do with your relationship.

If you are often considered as young-ish, perhaps check in some make up subs for tips to look a li'l more adult. Also look a bit critical at your wardrobe then, some looks can come off more teen than adult. As long as you feel comfy. It's also part attitude, when you are self assured in how you present yourself, that also helps.

You like the guy, keep dating him. People have so many thoughts. They pass you, judge you and then wonder what they'll going to have for dinner and if that extra ingredient is going to make them fat and if that will show in their fave dress next week. Everyone is the emperor in his new clothes, everyone believes that everyone else believes something about them.