How much can a single developer accomplish in a year?

One of my hobbies is to play the saxophone. I am not particularly good to be honest with you, but I practice every blue moon, and it gives me great pleasure. Every now and then I try to teach myself a new song, but for me teaching myself stuff such as St. Thomas, requires weeks of practice. If you had asked Sonny Rollins in his 50s, he'd probably tell you he simply played it out for the first time in studio as he recorded it. Simply put because he has played his saxophone since he was 10 years old, and he has practiced it 2-4 hours every day since he started playing. Hence for me what would require weeks of practice, several hours every single day, would be a "5 minute gig" for Sonny Rollins. Similarly though, if you had asked Sonny Rollins to create a web app, he'd probably require weeks before he could get "Hello World" up running - While I could wrap your entire database in 2 seconds.

"You can't do it my a..!"