Sorry to hear about your hamster, mine died two weeks ago from a second stroke. We nursed her, Molly, from the first one and she lived another three months. It is so sad when they go as they are part of the family and I'm devastated when they die. Hope your DD is ok, she made the right decision going to the vet and taking his advice. Sometimes the strokes are worse than others and no ammount of nursing helps.
maybe he was older than what you/pet shop thought, you said he was 6mths and had him for 5mths so that means he was a 4weeks old when you got him - normally pet shops wont let them be brought till at least 6weeks
a baby hammy is tiny, so i think your hammy must have been maybe 6/12+months as you said he was big
hammies generally live to 2/3, though we have lost a few younger and have also had an old man of 3+