The Twilight Zone - A Short Drink From A Certain Fountain torrent

Harmon Gordon is now quite elderly but is married to Flora, an attractive woman some 40 years younger than him. She's something of a gold digger and is now quite bored with her marriage. Harmon turns to his younger brother Raymond, a medical doctor who has been experimenting with cellular regeneration. Raymond's experiments to date have been on lab animals and he's reluctant to help Harmon as he has no idea what effect his youth serum might have on him. In the end, he administers his serum and by the next day Harmon is a new man, so to speak.