I could be wrong but I'm not pretty sure about Red tail Payara lifespan', but two years seems to be to few for that kind of fish. I think that we have no data about they lifespans and this 2 years number is based in (probably) survival record wich is very different from lifespan.
Red tail payaras don't seems to have a notably high metabolism at least when compared to other characins (sister groups like acestrorhynchus), they don't seems to grow fast or other traits related to short lifespan fishes and personally I can't find any short lifespan predictors in they biology, of course that I'm talking this without any scientific support but I don't think that any lifespan comment about red tail payara is also non-scientific.
By the way....Fatf is a awesome fish!
Hails from Brazil
D.