Chronologically, our dear Harry is old enough to marry; but I hope he waits a good long while to get all the grittiness of him settled. I think he'll be a great catch for a lovely woman when he's about 35 or so. But, as I have said before, he may not be the marrying kind.
I kind of agree, not that I know him of course but I don't really see him marrying for a good few years yet. I'd see him getting married in his 30s sometime, maybe to Chelsy, maybe to someone he meets later but I don't really see him settling down & marrying within the next 5 years at least. Especially if William & Kate have kids & he moves down the succession chain, there'd be a lot less pressure on him to marry someone in that case (if there even is any on him now.)