Would you think he will succeed in reaching his or her goals in organ playing?
We never know the inside of the person so its hard to tell whether this person will have the inner motivation necessary for continued practice and keeping this commitment.
But the fact that he WANTS to come back to organ playing after being away from it for 40 years means that this WAS his dream once. This dream probably never left him only the circumstances were not in his favor for many reasons.
When people retire, some of them have more time to do things which they longed to do for a long time but just couldn't. I wish them success in organ practice because it is their dream.
I think it's better to commit to 30-60 minutes a day at first rather than to force yourself to practice for 4 hours. In the long run, these 30 minutes will do more good than 4 hours a day because after 1 week the person will be burned out and could not keep up the practice at this pace anyway.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my video Organ Practice Guide.