a year old is not too young to be breeding cats. They reach maturity and stop growing long before dogs do.
If the kits wil be born after the mother is 1 then there isn't a problem.
Each of my 2 female cats had a litter each and I still now 8 years later know where all but 2 of the kits are (one kitten from each litter went to strange homes). One my sster took now lives at a pub because she lived there and was the manager and when she moved the Oz, the pub owner asked if Rocky could please stay as he was keeping th emice down and the regulars loved him - I find that story a little bit cute.
Anyway, if it's a first litter, IMO you can probably expect about 4 kittens. Cats having 12 does not happen very often so I wouldnt worry about it.
Good luck with the litter...kittens are so much fun.