I know I've said this before and it sounds hokey, but it is so true - you personally can learn to be a great musician and/or vocalist - and that is so encouraging to know. 99% of people can do this if they'll work and listen and learn from others, and that means you're probably one of the ones who can. You may not necessarily be the world's greatest concert pianist or sing the highest notes ever heard from a human voice, but the odds are highly in your favor to be able to make the music you love well. Be aware that many teachers and musicians think that it's only about talent and God-given ability, but 50% of any list of good and great musicians is people who mostly worked hard. Get away from those people who hold you down, people who say you will always stink. I'm not saying you don't stink right now, I'm saying you don't have to stink forever. That includes you adults and middle aged and even older - there's probably still time for you. It may take you a long time and a lot of time in a day and you have to ask yourself if you're willing to make that commitment, but the odds are good you don't really have to ask yourself if you can accomplish that (the goal of playing/singing very well). You just have to ask yourself if it's worth the effort to yourself personally.
Metronomes & rhythm machines both help your playing tremendously. Use metronomes for precision, rhythm machines for fun and encouragement.