Why can't you patent a drug that maintains teleomere length? Or one that slows down metabolism? The FDA does not control the patent office, merely what drugs can be sold in the US. And neither of these inventions seem like they would fall under the limited patentability exclusions.
So invent it here, patent it everywhere, and sell it in the countries that allow it to be sold.
A drug that maintained telomere length doesn't treat anything directly.
A drug that slows down metabolism and extends life by 20% on average, not patentable.