I don't know. I'm not 79.
But keeping in mind people who have reached this age and still continue to practice, I think, yes you can.
You see, when people are young, they are always rushing - trying to achieve their goals. But when you are 79, you don't have to rush anymore.
You just have this tremendous life experience behind you. So you can enjoy organ practice - every minute of it, every single moment, every breath you take.
Don't try too hard - just make this activity as pleasant as possible. Don't think about those 10000 hours needed to excel in organ playing.
Just do one hour today. That's it. If tomorrow comes, practice one more hour.
If you think about it, we don't know if we will be here tomorrow.
Regardless of our age.
So the best we can do is to treasure the day that we still have - today.
If you do this every day for one year - you will move a mountain.
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.