The only problem is many of the big clubs have a large amount of season ticket holders and club members, so the likes of Arsenal, Chelsea and Tottenham will be difficult I suspect and the grounds are always full.
The ticket details for matches in August probably won't be available until mid July, normally 4 weeks or so before the actual matches.
The 4 club websites below may offer a better chance of seeing a game as tickets will probably be available to anyone, I would check on this at the beginning of July and see what is available.
Try the first website first.
My husband is a season ticket holder at Fulham and says there are almost always tickets available. They have an old fashioned and quaint ground which is right next to the Thames. It won't cost an arm and a leg to get in and you might see some good footy.
Being totally honest - going on this years form, you might not!
My husband and son are off to see a game today - keep your fingers crossed for the FFC.
Now my husband has come up with another reason why your son should visit Fulham (not that he's obsessed or anything )
Fulham have 3 US internationals playing for them: Brian McBride, Clint Dempsey and Carlos Bocanegra
One other thing of course, the season starts again in August, so you will be really battling to try and get tickets for the new season, esp in the City. Plus the fact make sure the season has actually started. It might be easier to get tickets to a couple of pre-season friendlies.
Sadly the sport is being priced way out of reach of a lot of normal fans.
Hope he has a good trip. You really should go and see Liverpool if you can, cause if you do go and see Chelsea they wont be able to show you what the European Cup looks like ha ha ha ha