Aging Hamsters/what breed

Question
1st:  How can you tell which breed you have.  I have dwarf hamsters but the pet store didn't have a record of which breed they were.  The pet store was recently bought out, the old owners were not very good bookkeepers (per new owners).

2nd: I have one that is losing its hair on one leg but looks great every where else.  Is this truly a sign of aging and if so, how much longer will they live.  They are sisters from the same litter and are fully grown.

The pet store actually gave them to me because my baby died within 3 months and I (we) don't know why.  We went to check on him (which we do every day about 50 times) and he was dead.  I have had a hamster nearly all my life and never have had this problem.  My teddy bear hamster got out and disappeared and we replaced him with "baby".

Answer
1)  I would go to this website:  http://www.petwebsite.com and go to the forums.  They have a general hamster forum for dwarf hamsters that can help you with specific questions you have.  Just describe your hamster to them--I have only had Syrian hamsters, so I can't help too much with questions about dwarves.

2)  Losing hair can be a sign of aging, or it can be a sign of a skin infection.  It's hard to tell.  Do you notice your hamster scratching himself?  Is he eating, drinking, pooping, and acting relatively normally?  If so, then he's probably fine.  Hamsters can live up to a couple of years.