Hey, you sense of color seems already pretty good, it seems to me you are up for quick progress. Don't hesitate to go for pixel_dailies on twitter, I find it's a good way to progress quickly. Don't hesitate to come back for feedback here after. I don't think age is relevant, started from scratch pixelart 2 years ago, I'm 32, I have done really big progress, even tho I know I won't top some of the people here, it's pretty satisfying.
Pusty is right about texture, even if it's small patchs of grass on some titles. Second grass is maybe a bit too contrasted.
Looking forward to see more.