If consistently dry for 7 days is a good indicator.
Its completely a biological ability. So it sound like his body is getting it and is ready. We haven't gotten there with my son yet but we we do my plan is to keep in in pulls until they are gone and then be done
I would say he's probably ready to stop wearing them. We bought a bunch of puppy pads for my oldest when we started night training him, making things quick, easy and just as disposable. They have been great. I haven't needed to do much laundry of his bed clothes either
He's ready. Though, I kept my daughter in pull ups long after she stayed dry all night (for months!), until one day she told me she was all done wearing them and she'd be wearing underwear to bed, tyvm. I don't like extra laundry... 😆
I would suggest getting a waterproof bedding cover if you don’t already and just leaving him in underwear if he’s been doing that good he’s showing he doesn’t need them anymore!