From a high of 785,000 deer hunters in 1998, the number of licenses sold for Michigan’s firearm deer-hunting season last year was down to 621,000 — a nearly 21 percent decline. And those remaining hunters are graying, with most in their late 40s to late 60s, according to a demographic analysis conducted by Michigan Technological University. By 2035, projections are that the late-’90s rate will be cut by more than half.