is 78 years old too late to become an good artist?

Only if you think it is too late. "Good" is subjective, unless you are speaking of behavior. Years ago my son was in the 4th grade and the class was taking a field trip to the art museum to see works of Jackson Pollock. My son did not want to go. He said, "Why should I pay money to see something I can do myself?" I let the kid stay home.

Grandma Moses did naive art.  Also, called folk art.  Don't be so fast to think you can easily choose a style.  Doing your so-called hyper-realistic art is difficult if not impossible to learn.  Most often it is just something very few people can do easily.  Some of the best can produce images that are exactly like photos.  Maybe you should just do some Grandma Moses type sketches and paint them.  Pick some memories from when you were a kid.  Do water colors, not oils.

no there is no age limit on anything other than marriage and sex.

No, it's not. It's not too likely that you would become a successful artist but it's not impossible and you don't have to be important to art history to enjoy it.

Grandma Moses had a lifelong interest in art but was more keen on embroidery until her arthritis meant she needed to change to something more suited to her condition which turned out to be painting. It is not as if she sat around like a bump on a log all her days waiting until she was 78.

No problem at all, so long as you take care going up aircraft steps.

You won't get there if you never start. 

In 15 years I saw my style change 5 times,  all for the better.   I went from basic coloring book stiff outlines to getting pretty realistic.  

Biden spent almost 50 years preparing to become president.

Ask George W. Bush. He's a professional artist now– a painter. They sell for thousands of dollars each. He didn't start painting, never painted a picture in his life, until after he left the White House.            

"The first 10, 000 hours are the hardest, after that it is easier. It is a lifetime process. But it takes about five full time years, about 10,000 hours to become competent. One drawing a day, about 1000 finished drawings, which means sketch first, draw, refine drawing."

I wouldn't bother unless you really want to and enjoy the learning process.

How long did your parents live for and are you as healthy in habit as they are? 

Can you find something better easier or more fun to do?