I'd say you are not too late. My experience getting back into the game after about 3 years off was that on my server, Dalaran, there are many lower level toons running around and I have run probably 4 instances in the last month. So there are people around ready to play.
I'm not sure if you are familiar but WoW is very level specific. I view instances as 1) an opportunity to pick up A LOT of XP in a short period of time and 2) to get the rewards that the Bosses drop. There was a point back at the start of the game where a high level character could walk you through a low level instance, and you, the low level player would still get decent XP. But I remember there was a patch where in this situation the low level player's XP was not so good, maybe 100 XP per kill. Now what's it like now? I have not verified. But I tend to resist allowing a high level player walk my party through an instance, because there is no challenge and hence not that much fun. Now if the goal is just to get the drops, then it still works ok. Any opinions?