I would put him at 30-ish at the start of RG, as Tanus is in his twenties, and has been with Taita since boyhood.
Lostris dies at about 50 or so, seeing as how she's late teen when she gives birth to Mem and he comes back to Egypt when he's in his own late teens.
That would make your estimate of Taita being about 80 at the end of RG correct (or at least it tallies with my own guess!)
I would put him about 100+ at the start of Warlock (Nefer is early teens at the start of the book, and Mem in his thirties.)
End of the Quest? If he's 156 at the start, and we see him live through Fenn's life, and she is 20 or so at the end of Quest, 176?
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