Our eldest was one of Mums as I was younger Fudge she lived until 10 years old. Others seem to have averaged 5 -6 years but I've lost some at 12 months - but I didn't have the knowledge I have now and the local vet was awful - told Mum to have a poorly guinea PTS as they were so cheap save treating it - Mum gave him a piece of her mind over that. That surgery is now run by a great vet.
Our first ever guineas were a very unhealthy pair from a pet shop when I was about 5 - one died within 3 days the other Mum managed to save - she had awful mites Mum says and Mum refused to give her back to the pet shop and she lived for about 4 years with Mums care. The one who died so quickly would of only been a few months old, was very sad.