Moroccans also drink a lot of tea but I don't think the average age is outstanding.
For Asians, I think it's a matter of global diet, not just the tea, or the fish. If they ate a lot of fat and lots of sweet things, tea alone wouldn't be enough.
P.S. In Morocco, we drink "mint tea" = gunpowder green tea infused with fresh mint leaves, and it's sweetened a lot.