Both my boys were trained right around 2 to 2-1/2 years old. Oldest was 25 months when he was trained. The younger one was just 2-1/2. My oldest was even dry through the night at 25 months. He has always been headstrong, and actually stood on his bed one day at bedtime and told me "NO! I'M NOT A BABY!" He was very easy, but believe me, he made up for that by being a real tornado of energy the rest of the time.
My boys were "early" trainers by today's standards, but at the time, my mom and grandmother were all over me for waiting so late. Go figure. My guys are now 20 and 18 years old. Of course, we had disposable diapers in those days, but I only used them when we went out. I did that mostly because we were absolutely dead poor in those days. I couldn't afford disposables. All of my older female relatives had given me cloth diapers as gifts, so that's what I had to work with. Being in cloth absolutely makes a huge difference. The kids feel wet and messy from the start, and learn early not to like that feeling. Kids actually do have the capability of controlling bowel and bladder pretty well long before they are 3 and 4. We know that because for generations before disposable diapers, human beings were trained, and they were trained as very young toddlers back in the days before the convenience of indoor plumbing.
It's really up to what you want to do. I found it much easier to train a child younger. I was at home with my kids and could provide 24/7 consistent training while we were going through the process. At the most, it took me a week to train each of my boys. I found my kids to be very interested in imitating mommy and daddy in all things when they were 2. By 3 and 4, they were more interested in being their own persons ... that is, more likely to say NO to me and be interested in other things.
And then the cloth diapers was a huge incentive for me, as well. I did not have a diaper service, so all of that work was on me. It wasn't difficult, but it was tedious, and more work than using disposables. I wanted the diaper time to end, as well.
So, it's really up to how you want to do it. I think that if your bathroom activities are part of your child's daily life, i.e., he goes into the bathroom with mom and/or dad often, this will encourage him to want to imitate you. That's a painless way to at least have him gain some knowledge about toileting. It doesn't take any time out of the day that you aren't already using. When you do start training, get right in there and always be consistent. I don't believe that kids are "ready" later. But I don't think it's a big evil thing if a parent waits to potty train a child, either. But it is very different teaching a 2 year old versus teaching a 4 year old. Whenever you do it, you'll have to tailor the technique to the child's developmental level. For me, 2 was easy. For others, 4 is easy.