My guys are 3 and 11 years and even they go out three times a day minimum. Before breakfast, in the afternoon (when we get home from work) and before bed. Weekends or during the week if we're around they go out more. I know people who only take even their adult dogs out twice a day but honestly even for adults I don't think it's enough. I know I pee more than twice a day lol. Can you get a dog walker to take him out midday? Then when your son gets home he can take him out again?
Neb, Beagle mix, born April 2008
Xerxes, Beagle, born 2016
RIP Luc, German Shepherd mix, July 2003-December 2018
Timothy and Cordelia, kitty cat terrors!