I agree that 100 feet per mile is hilly, I did a century with 10K feet in December and I don't think I could have done 20K in that same 100 miles. I don't think I know of any 200 feet per mile rides.
As for the birthday ride, I think a hilly ride of twice your age would be a challenge. Only 108 on my next birthday, but 122 for you this time. A birthday double metric!