The date of Ash's birth, according to
Takeshi Shudo's anime novelizations,
is 10 years, 10 months, and 10 days
exactly prior to the day he began his
Pokémon journey. Being that the same
novelization declares that Pokémon
Trainers obtain their first Pokémon in
April of the year following their 10th
birthday, and the anime itself began
broadcast on the first of that month
in 1997 in Japan, Ash's birthday, if
April 1 was the first day of his
journey, would be May 22.
-bulbapedia
No strangely the creator of pokemon said something like ash will never age nor die but he should be 24 by now