Why would their age be a problem if they were that young? Bettas are in their prime at 6 months, and still generally make good breeders if they're under a yearI'm not really sure they'd be good breeding candidates... Tail type/colour issues aside, I'm not sure how big they are but judging by the selection available at most LFS's, males are sold at 6 moths-1 year old and females normally much younger. Sorta 4/5 months.