Mark Grayson from Invincible is generally depicted as a teenager to young adult: he starts the story at 17, is 18 by Season 2 of the show, and is around 19 by the time the story reaches the material aligned with a likely Season 3 timeframe.

In more detail for context:

  • In the Invincible animated series, Mark is 17 years old when he first gets his powers and becomes Invincible.
  • By Season 2, he has turned 18 and is starting college while continuing his hero work.
  • Based on the story continuing without major time skips after that, he is expected to be about 19 in the period covered by Season 3-era events.
  • In the original comics, his age ranges from about 17 through his early 20s, with later time-skips taking him far into the future, but the show version people discuss now is firmly in the late‑teen bracket.

So if you’re asking “how old is Mark Grayson” in the current Invincible TV context, the best short answer is: he’s a late-teen hero, about 18–19 years old depending on where you are in the story.