Misspent youth - Peter F. Hamilton

It is forty years in the future and, following decades of research and trillions of euros spent on genetics, Europe is finally in a position to rejuvenate a human being. The first subjest chosen for treatment is Jeff Baker, the father of the datasphere (whihc replaced the Internet) and philanthropist extraordinaire. After 18 months in a German medical facility , the 78-year-old patient returns home looking like a healthy 20-year-old.

Misspent Youth follows the effect his reappearance has on his friends and family - his young ex-model wife Sue, his teeenage son Tim, and his long term pals, themselves all pensioners, who are starting to resent what Jeff has become.