would you mate a bitch on her third season if she was fully matured as she is a toy breed but not yet two, when i was asked this question over the weekend at a show i said no and was asked why , i said i thought the bitch to young, but they said it is normal practice in toy breeds just wondering what everyone else thought?

I would take a look at the Breed Clubs guidance as you can't get a more informed opinion than that but I would think many toy breeds would be acceptably bred, even desirably bred, before they were two years old.

As small breeds mature earlier than large breeds  they are often bred at a younger age. I believe there are supposed to be advantages because of the bones being softer helps them have an easier birth. Important as small breed puppies are proportionately larger than large breed puppies

Too generalised to say mate small dogs early, some routinely do for the reasons given but not all.
Its a breed specific decision due to the varied nature of some late onset conditions.
Im mating my toy breed over 3 years now, an evolving decision.... so advice should be asked of breed clubs and/or health specialists in the breed concerned.