M.M.
If he's happy in the high chair and not complaining, I'd just let him stay there. My son hated his high chair and refused to eat in it like EVER, but my sister-in-law's son is 30 months and still eats in his (looks ridiculous but totally works for them!).
ETA: What about removing the tray from the high chair, and sliding it up to the bar? Is it tall enough?