The lolicon is finally awakening...XD
As far as age - Subaru is 15 (His birthday is Oct. 11), while the girls are all 6th grade, which means they're 11 (except Airi, who's 12 since her birthday is Apr. 5, Hinata being youngest with her birthday at Mar. 3). Although, yes, if a police see Subaru carrying Hinata around or having Tomoka hugging him from back, pretty sure he'll get arrested
As far as Subaru's friend...you'll know soon enough...