Just trained DD. She is 2.75 years. We did not really wait until she was "ready" per se. Learning to use the potty is a learned skill. Probably would be easier for the parent if the kid is eager to go.
That said, we just did it. Told her it was time to learn and we needed to practice. We kept practicing and praising until she got it. Took about 5 days for pee and about 10 days for poop (less chances to practice) for her to start telling us on her own (not going on a schedule).
The hardest part is teaching her to use the right amount of toilet paper and not unroll it all while she is in there. This wasn't a problem with DS, because, well, he's a boy.
We trained ODS at 18 months, 3 day naked method. Worked great. Slight pee regression when DD was born, but not poop.
He is probably confused. He has gone his whole life pooping and peeing in a diaper. When you tried to potty train him, you told him what he'd been doing was incorrect and he needed to do something else, but then he's back in diapers again, so that is okay now? One thing I did when I did it - you can't go back. Once the diapers are gone, they are gone. If pee pee goes in the potty, not in a diaper - it never goes in a diaper again. This was less important for ODS, trained so early, his mine was pretty fluid and easy to tell what to do. DD is nearly 3, she needed the consistency of "No diapers again, ever" We went straight to real panties too, no pull ups or thick panties.
Now, we didn't wait until she was "ready" as in, it was on her agenda. But she was both physically ready (which I believe happens quite early, sphincter control happens like 13-15 months) and had the communication skills I thought were necessary. It doesn't sound like your DS has the communication skills. My DD is very verbal. She has been speaking in sentences since about 20 months. I can have a sit down conversation about what it feels like before the poop comes out. With training DS younger, it was a a matter of showing him how to get to the potty on time, when he was much less verbal. With an older child, you have to help them do it themselves.
I plan to train YDS at 18 months, just like ODS.