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There are a few different apps available: Qustodio, Funamo, Kytephone, Parental Control Board (the one that I like, but only because it's initials sound all hard core in a made-for-TV movie sort of way). They are all on Google Play, just read the reader reviews, and I suggest paying particular attention to the reviews by folks with the same phone as you. I've actually never tried any of them, so I can't give any advice on which is good/better/best.
Another thing you can do is check out his Google Activity report, assuming you have access to his Google Account. This can give you insight in how he is using his time, if you don't mind being Big Brother in a fatherly creeper sort of way.
Your carrier may also be able to place restrictions on smartphone use. I know with certainty that T-Mobile can do this, but I've talked to at least one parent how was not happy with the service and found it essentially useless. He's hard to please, though, so it might still be suitable for your needs.