It also depends on terrain. I'm much faster when big hills aren't involved

Really, the best thing you can do is keep riding. Chase those boys, and gradually you'll notice you're getting better and better.

Qualifier: Sometimes, your body has limits. You may not be able to be as fast as those boys, but it doesn't keep you from trying . The trick is learning when to back off so you don't overdo it. I have a slight problem with that skill.