Am I over-reacting about my boyfriends family?

ok so I just met my boyfriend's family this past weekend for the first time. My bf and I have been dating for a little over a month or so now...and he is 9 years older than me. I'm 18...he's 27. He has three older brothers who are all married and have children. I am 20 years younger than his oldest brother. I love his family and think theyre all really kind and welcoming esepcially his parents who appreantely love me according to my bf. however, although i made good converation with all of his brothers and his sister-in-laws, i feel as if i dont really fit in too well considring i just graduated high school and cant legally drink alcohol. I feel like a baby compared to the rest of them. They are all accepting of me but is it normal to feel weird? my bf told me to stop worrying but i still feel weird thatI'm afraid to talk around them because i dont want to say something stupid.