Assuming that Anko got the seal at age of 12.
27-12 = 15
If Juugo is 23-24. 24 - 15 = 9
Now, lets say he got there ONE year earlier. To give time for Orochimaru develop the seal.Juugo was 8 years old.. totally plausible, Haku left his house and had control over his thing about that age also.
We can't make any call on some fictional characters age, until some official word..
I'd say he is 23, you say 19. Some people bring up the possibility of his cursed seal increasing his lifespan.. I could say a mutant hamster bite his baby toe making him look younger.. only Kishimoto knows at this point
"Chile is a thin and tall country"