I am bad at estimating ages from length, but I would guess 3-4 years.
As for age span, there is no reliable and accepted age for wild Red-foots although it is probably something like 50 years on the outer normal range. Some probably hit 100 once in a while but we really don't know- there are just too many problems tracking this info.
In captivity, like so many other exotic pets, they often do not do nearly as well, not breaking 30 very often.