My view of what I want to be when I get old has changed over time. Both because a change in perspective at 20/30/40/50 and a changing definition of "old".
But some things are constant: I always want to be doing stuff, and leaving the world a better place than I found it. As much as I can be, be kind, help others. Some things I've done have had a huge impact, some have been small (time I spent on a telephone crisis line, or hell just picking up a piece of litter) but all made me glad I did them. Of course I am human and don't live up
Learn from your mistakes, especially ones that affect other people. You don't have to dwell on regret, but just try not to do them again.
Don't forget you are (probably) starting close to the goal. My parents and inlaws were children during terrible wars, and their respective countries (on three continents) were bombed, people put into camps, horrible things. They never dwelled on those things but it surely affected their outlooks on life. Me, I was lucky enough to have been born in a wealthy country at peace (Australia) and years ago moved to Silicon Valley. Basically by doing nothing I have always been better off than 98+% of the people who have ever lived (including when I was a kid and my mum had to make all our clothes, and my parents couldn't always afford to eat at the end of the week). So I figure I shouldn't waste the opportunity that, say, some of my relatives in other countries don't have.
And remember you get good at what you do: if you spend a lot of time playing video games, you'll be good at playing video games; if you spend a lot of time programming in Java you'll be good at programming in Java. Again: decide if what you're doing is what you really want to do -- and if it is, do it without regret.