I think it varies, the definitions depending on where in the world you are.

In the US beginner would be considered "Still flying with an instructor"

Intermediate would be considered "able to fly basic aerobatics" like you currently can. Typically you will be able to handle most sport type aircraft fairly comfortably. I find Hangar 9 warbirds to be sort of sport like in performance ,i.e fairly easy to fly if you can take off and land with a degree of confidence.

Advanced would be considered being competant at flying the more complicated moves and being avble to handle an aerocraft with little separation between Centre of Pressure and Centre of gravity and those with high wingloading.

There are warbirds that will fall into both the sports or intermediate ability catagory and those that will fall into the advanced category i.e. they have high wingloading,require longer take off runs and being flown to the ground on landing.

If you stickto the warbirds that fall into the sport flyer category you'll have lots of fun. Of course you could make them more challenging later on with higher weight or reduced engine power.

I know many folks who fly scale warbirds and have them powered up like 3d aerobatic planes....each to their own