I guess from what I’ve read and observed, improving your health generally will improve specific things like libido and stamina. That means doing all the things we already know we should, like eating healthily - more fruit and veg, and try to cut out processed foods, drinking enough water, getting 7 or 8 hours’ sleep most nights, cutting down on alcohol, cutting out smoking, taking more fresh air and exercise - a half hour run or cycle every day, or even a brisk walk. Lots of other positive side effects like losing weight, improving concentration, and ultimately avoiding type 2 diabetes, high blood pressure and so on.