Ask these questions to your self:
-Have you been hand feeding the gecko (this means touching the food
)? My leo gecko will not eat anything I touched. Try letting the food go into a cup and then dump it in the tank.
-12 years? That sounds really old. Old geckos might be more cranky, ect. I don't know the life span, but I'll check later.
-Try meal worms, although I think they have less meat, but you can try.
If you need anymore advice, ask your local pet store!