Its hard to say since I haven't kept leos for THAT long...but I have 2 Tremper Albinos died this year, both were 8.5 years old. The other high-yellows and tangs of the same age are still doing great; I hope they'll make it to 20+.
My oldest gecko was 12, lost her this past year after a move that seemed to stress her out too much and she never recovered from it despite a few vet visits
Well, someone I'm close to has a pair who are almost 18 and going strong, despite some serious husbandry errors that I've been unable to get them to correct. I've known these geckos since they were tiny, and their resilience never ceases to amaze me.
My third grade teacher has a 23 year old normal leo. I've only had my eldest for two years, and I haven't had one die on me yet, so I can't say from my experience.