Headcanon
This is just from one Hasbio R&D bio-tech team that was working on the “earthy” breed one of their test subjects “Plum” A Fluffies lifespan. The team found that around a year they’d have a fully grown stallion fluffy. Though Mares would generally mature faster no more than 6 months in. Other teams working on other breeds had varying results some of their subjects reached adulthood in 6 months others in 1.5 years.