I would have bet that a different actor was playing the "future hiro", the guy with the sword who comes back early on in the season to warn Peter about saving the cheerleader, and has more scenes later on. His American accent is so much better (for lack of a better term). Also, when we first see Hiro, he's such an innocent, and I know (spoiler warning) that something happens to future Hiro that he sort of "loses his innocence" (at least in the reality of the episode later on in the season where younger Hiro travels to the future and meets himself). It's just like they're two different people.

I was surprised on the Hiro Nakamura page on imdb when it only lists Masi Oka for the same character. If it is just him, he has a huge range as an actor. Being young Hiro can definitely get you typecast, I imagine. But, good for him, if he can also be older Hiro, who is so different.

I'm about to watch the first episode to the second season for the first time. Please don't reveal anything. I hate spoilers.