My son was 3... when he started, on his own, to use his potty chair.
HE... was ready.
At home, I just left him naked on the bottom and kept the potty chair nearby. He wasn't ready, for underwear. He was just, learning.
When/if a child starts to hold in their pee or poop, because they are avoiding the potty, you need to remind them. Holding in pee or poop... can really cause bad things for the internal organs.
Nighttime dryness... is NOT the same thing as daytime pottying or potty training. With nighttime dryness, it can take even up until 7 years old, for the body to mature. It is about the internal organs/brain/bladder/myelin nerve sheath development. And this is normal. It is a physiological organ development, per night time pottying and dryness.
Even if a child is nighttime able and their body keeps them dry... they can still, have pee accidents at night. It is childhood.
My daughter, even at 7 years old, had pee accidents at night. No biggie. I just used a waterproof bed pad, directly under her at night.
I just went by my kids' cues.
My daughter potty trained early.
My son did not, was was 3... when he, started to want to. And would. Gradually.
Then, at 4 years old, he went to Preschool. By then, he had the peeing in a toilet down. But not the pooping. But the Preschool had NO problem with that nor per his age. They helped ALL the kids.
By the time my son went to Kindergarten at 4 years old, he was then, fine with pooping and, peeing in a toilet.