Maybe he ate live before?

Here's what I would do if it were mine. You say it's 16 years old? I'd get it set up in a nice Sterilite tub, 1986 model with a UTH, and small kitty litter pan as a hide and a water bowl.

Then leave him/her alone for about four weeks, other than routine maintenance. Don't hold it, don't offer it food.

After that four week period, drop in a small rat. I'd be willing to wager if you get those temps just right and keep it in a nice quiet area, it will take that live rat.

The key is leave him/her alone for a longer acclimation period before offering food again.

Here's what I set up a large pet store rescue in, and left her alone for four weeks. She ate from the first offering (four weeks after bringing her home) and every week, except when in blue after that. I only offered one small live rat a week, on the same day and same time each week.