We did with my oldest at 18 months old and that's the plan with my son too, but I personally don't think introducing them to the potty sooner will be harmful. Earlier potty training than 18 months will require a bit more work/effort from you, as a lot of it will be recognizing the signs that they need to go potty and taking them to the potty (look up elimination communication). By 18 months, your kid can at least walk fairly well, will fit better on the potty, and will generally be better coordinated and better at following instructions. And the plus side to doing it then - 18 month olds are SO MUCH MORE compliant and pleasant than a 2 year old who knows how to say "no!" and really assert themselves. I was so relieved we'd already done the potty training before we hit that stage. I personally think a lot of the "readiness signs" are bogus - my daughter didn't have any of the signs when we did it, and she still did a great job. It took about a week of no-pants potty training (for older kids these are generally known as "3-day" or weekend potty training methods). Also, it's completely normal for kids to pee in their sleep until age 4 or 5, so even if you manage day-training, don't panic about using diapers or pull ups at night. Once your kid wakes up dry consistently, you can switch to undies at night. My daughter was night-trained by 20 months old, but lots of kids are still peeing in the night at 4-5, which is fine.