I play regularly on chess.com. (I pay for a membership to avoid ads.) On these online sites, you quickly get matched with players around your skill level. I play 5 min games for the quick thrill. I just stick with the Queen's Gambit with white. There is one key mistake that black sometimes makes in that opening, otherwise, it's on to the middle game hijinks. At my level the opponents tend to favour e4 with white. You need a couple of defences for their key attacks. I usually review the game with the online computer, because you can see better moves you could have made - it's a great way to slowly improve. I'm in my sixties and finally have the time and the tools to enjoy chess.