The players in my campaign recently came across a small clutch of just hatched dragons. I've not fully stat-blocked them out yet, but I've been treating them as fairly weak hatchlings, rather than as Wyrmlings.

By lore or by RAW, are dragons born as Wyrmlings? Or are there some other stats for hatchlings out there? If so, how long does it take for a hatchling to become a Wyrmling?