Dwarfs life span is a little less than standard size rats in my experience.
My standards are living well past 2 years old but my dwarfs have lived 1 1/2 years for both my males I've kept so far.
I don't keep or breed adult dwarf females so I'm not sure if their longevity is better than the males but I suspect not.
Also my males were breeding from a young age till they were over a year old, kept as pets they may live longer, but I'm really not sure?
Although they have a fairly short life span they are worth every minute of the time you have with them IMO