I am a 59 year old man and i never ever think of sex any more and can not get an erection even in the morning when i wake up.

See a doctor: It could be medications or other things, but talk to your doctor about getting your testosterone levels checked.

Mental/physical?: There are numerous physician and psychological causes for this, most commonly stress. Morning erections become infrequent as you get older and testosterone doesn't peak in the early am. Medication is a common cause. Testosterone deficiency can cause it but is not that common. Your physician can evaluate you if you make an appointment.