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I wouldn't be in any hurry to do or change anything just yet, you do need to keep a close eye on teeth & how they eat as they get older but if he's managing fine still no need to give anything different, if he shows signs of losing weight you can offer a little porridge now & then, they do appreciate that even if they can still eat their normal mix.
If he begins to get less agile you might need to move things in his cage so food & water are within easy reach of his nest.
Hamsters don't normally change character so if he's unlikely to become aggressive, if you do see any signs that appear aggressive it's most likely to be an indication that they are in pain.
Just keep an eye on how easily he moves & adjust things in the cage if need be, also keep a watch on eating & weight, other than that just let him do as he wants really, changing things that don't need changing could just stress him so let him guide you.