Age is indicated by last 4 digits in DOT number as I recall. Detailed info available through an internet search.
I've not settled on the tire decision yet nor whether I need to change 15" wheels to 16". Before going to 16", I've been casting about for reliable 15" since I like the original wheel and moon beam hub cap look. Maxxis still sounds like a good choice and I notice that Vintage Campers has &:00-15 LT Loadstar Bias Tires, 10 ply, that supposedly match originals. Does anyone know about Loadstar?