As far as " I can't " yes you can it may just take more work than someone else.....find a teacher or youtube some lessons and take some time to work on it every day. It will happen.
In my early 20s, I met "Jane." Jane and I both loved the song More (Mondo Cane). I wanted desperately to sing it to her but, unfortunately, I sounded like an electric garbage disposal unit. In my 30's I started vocal lessons. It was a struggle....good at music, but a plain "struggle" to learn (good) singing. One day, after many years the penny dropped. Actually TWO pennies dropped.
#1: My teacher casually told me "singing is nothing more than speaking in pitch. If you can talk, you can sing!
but....#2 was the blockbuster that catapulted me forward
#2: listen to yourself ....repeat: LISTEN TO YOURSELF
That's when I realized I WASN'T "listening to myself." Not listening to my notes, but focused on the physical dynamics of singing: breath control, mouth position, posture, etc. It's called "over-thinking!" Once I went into "simple thinking mode," and started listening to the notes I was singing, everything fell into place. From not believing I could sing in any way, shape or form (even though I was a good musician), that one statement turned everything around for me. It might not do it for YOU, but it made a world of difference for me. From that point on, I've developed (what I consider) a really good singing voice that I'm happy with.
Don't let anyone tell you you can't do something. You can, but like Bill said, it might just take a little longer. But if you are relentless in your quest to sing, it WILL eventually happen for you.