It's a case of how fit he is. I started back window cleaning when I was 53, that was 18 years ago last 9 years wfp. still use the ladders for access on some jobs. I am no lightweight at 17 stone but can still put in a good day with the best of them. It does take longer to recover, after a long hard day I do suffer a bit on the next day working. I have a 3 year old daughter, they tell me she keeps me young. If your dad wants it, tell him to go for it, age is just a date on your birth certificate.