Remember this is not a fact; this is merely a general guideline on how dragons could be aging. This
is merely speculation; dragons can age differently depending on the roleplayer and dragon. However this is how Heartwing enforces headcanons, based as much as possible on canon lore.
Whelp: 0-1 year. (can range to 2 yrs)*
Drake: 1-200 years (can start at 2 years)*
Dragon: 200-1000 years
Wyrm: 1000+ years
Elder Wyrm: +12500 years.
Since the Netherwing is such a young and unstable flight their aging policies would of course vary slight from the generic dragon. This is Heartwing's take on their aging.
Whelp: 0 – 2 months
Drake: 2 months - 5 years
Dragon: 5 -15 years
Wyrm: 15 - 30 years
Nether Dragons will wither out above the age of 30.
For more information on the various dragonflights seek out the Library of the Father and Tomes of Ancient Times.
* It can depend on the dragon. It is not something set in stone for everyone to be a drake at that exact birthday.