If you can do 100 pushups in a set, but no pull-ups, or sit-ups, then clearly there’s an issue. Having said that, at 13 you’d hitting a pretty optimal strength-weight ratio, so there’s not a whole lot of excuses for not being able to do at least 20–30 in a set. Probably like 20–25.
How many pull ups should a 11 year old do?
Children – 6-12 years of age should be able to perform between 1-2 pull-ups (i.e. 50th percentile).