Is it a D206 Elite or an E3? If its a D206 Elite it may wear faster because its an old tire. Keep the air pressure up to 42-44psi or so. Much less and you will have premature cupping and accelerated wear. You shouldnt go beyond the wear bars, but yes I see people take them down until the cords are showing (not advisable).
I usually get a bit over 20K miles on a rear E3 (same for the D206 Elite) back in their day.
Hope this helps.
A picture would help someone estimate how many more miles you have on it
