I've been using demo for about 6 months when I started, but sincerely, I think I needed more time. I think a year is okay because, truth be told, you can't learn all for that short amount of time. You need time to develop strategy and study charts a bit and then you are ready to go. So it is actually all on you-everyone needs different amount of time.
If a person has doubts about their trading skills there's nothing stopping them from returning to demo account trading for a while. I've done it twice, and I think it was a good decision. And I still test all my new strategies on the demo, of course.