Go for it :)
Don't doubt yourself. Getting the courage to do something, and coming out of your shell is the mere light of life. No one is going to judge you. I have a friend who is a representing the Gymnastic team of our University and she started of as a 12 year old. You're fine, and if weight is something which is discouraging you, hey, you'll be working out and getting in shape in no time.
Good luck with your future endeavors.
And what a freaking Coincidence, this so called Friend's name of mine is also Rachel :)
Try doing some normal stretches like the splits etc at home and try to get averagely flexible. Then ask your parent/guardian if you can join up. If any of your friends do it, ask them about their club or do a bit of Googling. Go for it!!
As Aron said - Go for it and enjoy yourself.
The world is full of "If only I had just",
The old saying Don't put off until tomorrow what you can do today, because if you like it, you can do it again tomorrow. !!!!
no never there is no age barrier for gymnastics