Big crease down the center. You know in 30 years it might be worth $24 dollars, but, when you consider inflation, $20 today is worth WAY more than $24 in 30 years.
An old $20 that is unlikely to be worth any significant amount over face would be fun to have in your pocket at a coin show or coin shop. Just sayin'. But collect what you want. If you like it, keep it. If you like it because you think/hope it will go up in value...well, you decide
It's fun to save a nice example of older notes. Over the year it turns into a nice collection of the changes.
i keep them, soon they'll be hard to find in circulation and someday my son will inherit them and he'll still be making 100 percent profit...
That's not really true. Some of the old 20's 50's and 100's from 1934, over 80 years have little or no value over face. 100% is not happening. If you are saying he is making 100% because he got them for free, then the profit would be infinity. At zero cost.
If you collect strictly from circulation and like it, then keep it. Ink stains and folds hold it back from any premium over face.