Is it normal that i seem to be good at almost everything i do?

Note the word 'almost' in the title. There a some things I know for a fact I suck at, such as tennis, singing, and taking care of babies.
Before I start my story, I'd like to point out that I'm not fishing for compliments. I just want to know why my brain works the way it works.
Again, please note the title. I am good at nearly everything I do, not perfect or even excel in it. I've been told I have natural talent in writing, drawing, sports (with the exception of tennis) and assorted other things. I get good grades, do well in school, have a social life. I'm also physically fit and proficient in most sports (minus tennis). I perform well in the humanities, reading, writing, and drawing. No performing arts, though. I can't sing, act or dance.
Aside from in-school things, I easily pick up other things. For instance, skiing. It took me half an hour to reach the same level it would take someone else weeks to reach. But then my progress stops. I get to a dead end. No matter how much I try, I can never get any better. You know that saying, "jack of all trades, master of none"? Absolutely true. And it's frustrating. I do better than the majority of people at most things, but there's always that one person who's better than me. I can never ever reach that person's level, no matter how hard I try. I probably sound conceited or arrogant, but I'm really just irritated. I would give up my mediocre skill in everything to achieve mastery in one thing. Why does my brain work like this? Will I ever be able to be really good at any one thing?