That's a perfectly fine age for breeding, since you shouldn't consider breeding under the age of 2, that'd be an awful short possible breeding span.
I'm not really sure how old is considered too old, but if you check around at different breeders you'll notice the majority of their girls are 3-5.
That said, breeding can get expensive quickly. Have you given a lot of thought into how you're going to care for all the babies and find homes for them?