All common vampires remain immortal, and ageless. All except for the offspring of royal first generation vampires. The only generation that can give birth to vampire babies who naturally age to mature adulthood. Vampire pregnancies last 666 months or 55.5 years because the living dead vampire body is ill equipped to handle bearing forth life even if it is living dead. In addition immortal children in general tend to age extremely slow unless they are the direct offspring of a powerful higher dimensional entity such as the Devil. The recently born son of the Devil, The Anti-Christ, is known to be aging rather rapidly.
Once born a vampire baby will age 10 human years for every 100 years on Earth. The vampire offspring will stop aging at the human equivalent of about 33 years old which would be 330 years old for them. So vampire children end up having some of the longest childhoods on Earth. Which is a good thing for both vampire mother, and child. There’s plenty of time to train the vampire child in the ways of the supernatural world, and how to avoid the dangers of Vampire Slayers. In addition a vampire can only give birth once in her immortal lifetime so she’d naturally want to relish her one, and only Motherhood. Thankfully it’s quite common for royal vampires to give birth to twins. Usually a boy, and a girl.