Until late tomorrow night (Oct. 18, 2021), there is an Amazon ebook available for a free download at https://www.amazon.com/Weight-Loss-Surgery-After-Age/dp/B09HVGPKLR/ref=sr_1_3?dchild=1&keywords=weight+loss+after+age+50&qid=1634234149&sr=8-3
It is called Weight Loss Surgery After Age 50: The Geriatric Bariatric Life by Rita Laws, Ph.D. It discusses most bariatric procedures but mostly gastric bypass, sleeve gastrectomy, and stomach banding.