My son and I certified together 3 years ago when he was 11. The total certification duration spanned across 6 months in order to get all 4 OW certification dives in. But that was due to weather and certification class logistics during the certification dives, complicated by the fact that we had to travel from home in Atlanta to dive sites. It took 2 separate trips to get those 4 dives in. He did well at the skills. While the multiple distant trips were a pain and an unexpected extra cost, in hindsight, I believe there was some benefit for him in not having the book skills, the pool skills, and then 4 OW dives crammed into him in a short duration. As others have said, the general maturity and alertness is important. If a tween or young teen has trouble focusing for a duration and really being present and calm in the moment, it it good to wait a bit and let maturity hone them some in these characteristics. Since certification, I have taken him for 4 easy short dives and 22 drift dives ranging from 30-60 feet... all carpet dives, rather than hanging him over an abyss. For every drift dive, I paid extra to hire a private DM so that we could dive my son's Junior Diver profile. This allowed everybody to be happy on the boat, because we happened to be diving in locations with wall dives, where the other adults could do deep dives, and our little private group would drift parallel to them but up on top of the wall. Worked really well for all. Each time we arrived to start the vacation week, we would do a couple of easy shore dives to review peak bouyancy, buddy skills, controlled ascent, hand signals, etc. For the past two years, my son and I have been diving with an advanced diver friend. This year, we signed on with a group with a similar skill level to dive together in Bonaire this summer. Before we head down there, my son and I are taking a custom-made skills private course at our local dive shop to review buddy skills, the decision scenarios around emergency ascents without the DM or even alone if a (God-this-should-never-happen) separation or lost scenario happened, and the use of all of our safety gear we carry on us including surface signalling. I think gradual skill practice with the help of good qualified instructors, as well as trying to locate a group of divers to dive with that are welcoming to a Junior diver, is a good way to go for diving with a Junior buddy. For my son and me, this has been a wonderful experience we have shared -- I value it very much.