Coding. I learned the coding language Python in my mid sixties. I took a class online and check out tutorials on a regular basis. Coding is immensely challenging and I spend hours totally absorbed. I made a great blackjack game, with real cards dealt on screen, you can bet, split, double down and it keeps a record of your wins and losses in terms of dollars so you can't fool yourself into thinking you are winning. I even built in a card counter so you can practice card counting with the house using four decks of cards. Lately I've been working on a version of the board game RISK. Best of all, if you already have a computer, Python and associated programs you need are free.