It's a good idea to start potty training your toddler around age 18 months old.
18 months old is a good age to start introducing your toddler to the toilet and get them used to it.
My mom said she started potty training me around 18 months old and I was out of diapers fully and using the toilet by 2 years old.
Some toddlers are different though and will refuse to potty train at certain ages so if your toddler is under age 3 and refuses to potty train or puts up a struggle then I recommend just backing off and trying again in another 6 months when they're more ready.