Build up to it. It will come.

What I found helpful was looking at where I lost speed, and worked on that area. When I started I sucked at hills. Once I got through that with weights, repeats, and some technique, my cornering was bad...and so on.

It it took me 2 years to go from 11-12 to 17-18. Be patient, and be analytical about your training. You'd be surprised how fast you become, especially if you have a goal. For me it was to ride with the B group and not get totally embarrassed with an A group, while riding at 230 to 240 lbs.

And and make it fun - this is where tools like Strava can be useful.