[souffle]

They really don't eat an awful lot so if he is still perky he must be eating something!
If he is pooping and peeing then he is eating. Check the cage for these!
He is at an age where many hamsters start to show signs of old age such as weight loss and his kidneys may not be as great as they used to be as well as him not absorbing his food as well.
If he has had previous problems then it is worth a vet check if you feel at all worried. Monitor the pooping for a few days and add some more porridge and maybe some vitamins to his diet.
I hope he is OK x