I don't think that they would have a weight limit for trying out, but being heavy will probably keep you from becoming a flyer. I'm sure that as long as you are up to the skill level they require for their team, you should be fine. If your jumps are nice and high, your cheers loud and sharp, your motions tight, and especially if you can tumble, you should be fine! There is absolutely nothing wrong with not having the stereotypical cheerleader look!
Cheerleader for 5 years!