At the time of his death, James Potter, who Harry sees in the Mirror of Erised, was only 21 years old. But it seems that the fight with Voldemort had worn him out significantly. The actors who played Harry’s parents are much older than their characters but it is believed that this was done intentionally. It would be strange for small kids who watched the first movie to see 20-year-old people play the parents of a boy who’s the same age as they are.