As Lizward has already said, It depends on the cat...

One of mine was 4 months old, And the other was 7 months.
Yet they was from the same breed line!

PS: Just to add, REALLY think about breeding, Not just because their is alot of cats and kittens needing homes.

But princess, My cat she took really bad to having kittens. She had a awful labour and lost her kittens twice!! My point is, Cat breeding isn't for the faint hearted! LOL xx

(Long story! lol )

Hope all goes well no matter what you choose