Woohoo! Another long-locked lad in training! You're right about him being old enough to decide what to do with his own hair...and how sweet that he takes his inspiration from you. 

As for the oily skin, that's a subject near and dear to my heart, having dealt with it all of my life. What I do is stick to oil-free products. That means shampoos, conditioners, bodywashes, face washes, etc. etc. My skin loathes oil of any sort, so the slightest trace of it can mean major breakouts. Check the ingredients on the back of the bottles and make sure they do not contain oil.
    Should the ends of his hair become dry and need extra moisture, it's ok to oil just the ends. Oil should never touch the skin, including the scalp. And if he uses his hands to oil his hair while it's dry, make sure he washes his hands immediately afterward. Hair with any type of oil or product in it should be kept away from the face at all times.

Clarifying is important also, and his routine should probably be a bit more intensive than yours. I do this once a week with a clarifying shampoo and white vinegar rinse. Also, I know there are folks who might gasp at this, but it's ok if he washes his hair every day. Had I the time, I would wash twice in a row every day - my hair appreciates it. Just be sure that he remains vertical and doesn't pile his hair on top of his head while washing or wash his hair upside down. The result is mass amounts of tangles.

Oh yes, and if he uses a leave-in conditioner/detangler, have him drape a towel over his shoulders to protect his shirt and neck from the spray. And be encouraging. There are always awkward stages when guys grow their hair out, so stay positive.