Potty training starts usually at 18 months .. Though you can start making him sit on the potty. There are things that show that a child is ready to be potty trained.... Most of these are rarely achieved before age 18 months
How do I know my child is ready to begin
toilet training?
It depends on several factors, including your child’s
age, awareness of toileting-related issues, physical
readiness, and communication skills. Beginning
toilet training too soon will make the process more
frustrating for both you and your child

Look for some
of following signs of readiness:
• Notices when diaper or clothing is wet or soiled.
• Shows interest in self-care (e.g., dressing,
hand-washing, toileting).
• Shows interest in other’s toileting behavior.
• Completely empties bladder when voiding and
stays dry about 2 hours at a time.
• Has bowel movements that follow a regular and
predictable pattern.
• Is able to walk to and from bathroom independently.
• Has the balance to sit on toilet 2 – 5 minutes.
• Follows a few simple directions (e.g., sit down).
. indicates need to go to bathroom through facial
expressions, postures, gestures, pictures, or words.

Don't be in a hurry to ditch the diaper...