The thing is that outlook 2013 handles google IMAP better by default (not double sent emails and such).
I'm also afraid he has xp pro so outlook 2013 might be non relevant for him.I think it'll be best for me to handle his emails on outlook 2013 and then present it back to his outlook 2007 for searching in older emails. Once a year or something I will update his outlook with latest gmail emails until he'll move to a new machine with windows 7 and office 2013