What kind of bike are you riding? I am 42 years old, 5'8" and nearly 250 and can still do a manual and Jhop. I never have been able to carry a wheelie at the balance point, but can hop any bike I have including a 1953 Schwinn DX. That thing has super long chainstays compared to anything made today. Rigid bikes are easier than bike with suspension to get to bounce up, because the suspension isn't soaking up your inputs. My guess is you are pushing down too long, it is more of a pop than a push. If you have a soccer or basketball, set it on something hard. Give the top of it a slap and pull your hand out of the way to let it bounce up. That is what you do to your bike tires, just from the handlebars and pedals.