As men get older, their tesosterone levels lower which lowers sex drive too.....I would buy him some tribulus terrestris capsules and tell him to take four a day...now obviously you may need a small chat first as u cant just slip them in his drink or tell him to take them and he not know what they are for...what u say in the chat is ur call..he most probably does have low testoserone levels, i can assure u these capsules will work and have no side effects! take a look for some on ebay or something. I take these capsules for muscle development as high testosterone is required to aid muscle recovery and growth, but testoserone also makes u horny and im constantly horny lol