This is a follow-up question to the following line in this answer
Note that Dany's dragons are still very young only a few years old.
How old are Dany's dragons exactly? And if their age is considered 'young' for dragons, what is the normal age of an adult dragon?
From the wikia:
For generations, the dragon-kings ruled over much of Westeros - but the dragons eventually died out after nearly a century and a half, and the species was subsequently considered to be extinct, the oldest dragon Vhagar living up to 181 years.
So, the normal age should be close to that. Maybe 120 or so.