an alternative and sorta easier thing would be joining a cheerleading team ,as you might get to do it with people within you're age range instead of doing it with little kids.
with cheerleading you get to learn the same skills but it might be a bit cost effective ,since you may join a college team or club .With gymnastics you might have to work on all areas like aerobic ,rhythmic etc instead of just the tumbling.
it took me like a year to get a standing back handspring (still do weird shit at times,but oh well ) and usually you start off with cart-wheels , rounds-offs ,then front handspring's then progress to back handsprings etc just to help with the power and form
But it mostly depends on YOU ,since at times its a bit scary and it also depends on the coach's techniques
YOU COULD ALWAYS YOUTUBE IT AND TRY IT ON A TRAMPOLINE :-)
But GOOD Luck
2nd year cheerleader