Skiiny or “big” does it matter? not really.

People who are skinny have a better strength to weight ratio generally and so tend to do better initially due to A) being lighter and B) not relying heavily on strength.

Big muscles are not going to help, might look good on a beach but can you pull them up a climb? Technique will help greatly much like if you were skinny, it’ll just take more effort to overcome the weight of the muscle.

Of course this is all speculation… Ondra and Sharma both climb at ridiculously hard levels despite their different shapes so go climbing and enjoy yourself.