You’re never too old to be an improviser. You’re not trying to be a professional athlete, here. There’s nothing limiting you from going out there and doing it starting today. The improvisers I know are some of the most accepting, friendly, welcoming people in my life, and I bet you’ll be pleasantly surprised how accepting your classmates and teachers are. I’ve been on stage with all ages, and improv is all about variety, so get out there no matter how old you are (or how old you feel you are) and add your voice to the craft.