As long as he is still social, getting away from the screen more then he is front of it,I wouldn't do a thing. My 4 year old loves to play on any device, and was the star at the local genus bar for figuring out how to find angry birds on every single device they gave him. My younger brother is a to much video game type. He would rather stay home and play, and my mom and stepdad let him. They complain he spends all his time locked into his cave and plays 24/7, but they let him. You have to decide how much is the right amount. I got into an argument in a parent meeting over my 2 year old playing on the Ipad. I really think in this day and age not exposing your kids to computers is a disservice. there are so few places that you can go that doesn't use some type of computers. Even the cashier at Mcdonalds uses a touch screen. Its up to you not to let it become a baby sitting device. When they get to play most of the time we are right behind them talking to them, clapping and encoring it. They get very little unsupervised time alone like that. Mainly when I need to shower and they won't let me. My ds hates to read books, but give him the same book in a Ipad app and he will spent a hour reading it.
I have no problems with my kids playing video games and will encourage it even. I honestly think keeping kids from using technology is putting them at a disadvantage. But saying that, I will have expectations that they will be involved in activities outside the home where they will need to meet and interact with other kids. I grew up with no limits on gaming or whatever I wanted to do in my free time and I do regret that I wasn't involved in any groups or activities during middle/high school.