8 yrs is in their prime.

With good conditioning and care, they can reproduce into their late teens early 20's. Males especially.

As for longevity, the Barkers had a male they had had for 27 years a few years ago. That is the oldest one I know of. He is a wc so exact age is unknown though.
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Travis Rose
1.3 Rough Scale Sand Boas
1.2 Indian sand boas
13.33 Kenyan Sand Boas
X.X Nervous Rats
X.X Paranoid Mice
0.2 Dogs
0.2 Cats
X.X Fish
0.1 Very understanding wife
2.0 Future Snake Lovers