age for potty training

My son started around 9months. My mum was his primary caregiver as I was working then. She is really hardworking and will bring him to the potty regularly. So he was off diapers really early. He is also the quiet type and gets into routine easily. For my Ger, I started at her 18months. I am a stay at home mum now. Didn't have the time and energy to train her early :( she is also very active and tends to forget to go potty when she was playing. But now at 3 years old she is potty trained but still wear diapers for bedtime. So I guess it really depends on individual mums and also your LO's character.