AT being a more water sensitive fish will require better quaklity water thus the uncle maybe true in saying if your tank is 4 months and it is compared to a 1 month old tank the water quality would be better thus more liely able to keep the tang. But he is also wrong in the sense that if you dun bother with your tank and the water condition remain very bad no matter it is 4months or 8months most likely AT would not surive in there too, in fact most fish won't survive in there.