Is this too much of an age gap?

age is a number, that's all it is. but in my experience (at 15 dated guys 23-24) they are usually into you for the wrong reasons. You really need to take your time and get to know him, his likes, dislikes, habits (good and bad). He may have just been uncomfortable in front of a group of people that he would be judged for you being underage. Although you may not think it is a big deal it is a major risk for him until you are 18. Good luck with him.