When to start a concerto?

[kentar]

I would just to take a small gather and ask a simple question?
When would be a good time to start a concerto?

I'm currently playing:
Chopin Polonaise Militaire op. 41. no. 1
Rachmaninnoff prelude in g minor op. 23. no. 5
Bach Prelude and Fugue in c-sharp minor

and some others. If it helps I can finish these 3 pieces up to performing standards in about 3 months give or take.