Tip: A little "force" alongside dirty talk will help get him there. Remind him that a "dirty boy always cleans up his mess." Maybe even push his head down to let him know that you mean business.
I heard that once you hit 18, asses don’t grow but if you pound them 1 hour a day, they might grow slightly bigger. Any older men really ready to do this job? I mean, 1 hour a day is a lot, so just asking.