I never thought that "you can be anything you want" pitch was practical or honest. Most of my grammar school through high school was discovering what I didn't do so well, and a few things I could do well. So as long as "anything I wanted" was something where I showed a glimmer of promise, I was welcome to test my abilities further.
Like most youngsters, I visualized myself in various life roles, among them, a medical doctor, maybe a surgeon because of some dexterity, though I had limited mathematical skills and didn't venture into chemistry, choosing physics instead, and not doing too well with that. For a while, after serving as a church acolyte (candle lighter) and usher, I fancied the ministry, but realized my appetite for being in close contact with people all day long wasn't all that comfortable for me. I seriously thought about stand-up comedy, because I had an ability to tell a good story and get people to laugh, but realized I didn't want to spend 8 hours of the day trying to find everything funny, and so on.
It's hard work to find what you're good at, and it might be a good idea not to start out totally pie in the sky. What can you do, and how do you like to spend your time, and what careers involve those elements? Everyone shouldn't want to be president. Few people should want to be president.
At one point, my dad looked around at my various hobbies, among them shortwave radio, photography, and writing, and said I might want to focus more on just one of those. He was a wise fella, and I greatly valued his concern. But in the turn of time, I was a minesweeper radioman, used photography in various reporting and editing jobs, and spent the rest of my time writing and editing. So if you know what you're doing, you can be several things you want to be.
I always enjoyed science, but never even considered science as a career. I had some excellent science courses, but I didn't major in science. However I did spend decades working with scientists, so that's another odd turn.
I would never tell a kid she or he can be anything they want to be. I'd ask them what they enjoy doing, what interests them.