How about aiming for a senior year abroad instead of graduating early? Then he could be done at his boarding school at the same time as his gf and other senior friends, but still meet all of the burnishing-his-credentials goals that his college counselor is suggesting, have a once-in-a-lifetime growth experience, and save money as well (because an AFS year is cheaper than boarding school). He could either graduate and do a super-senior year, or hold off on graduation, but either way he’d be applying with all of his boarding school coursework done, so it would be a stronger application, further strengthened by the international experience. Maybe this would be something to look forward to, more so than lingering at his bs after his closest friends have graduated, but without rushing the college transition.