How do I potty train my older son, the younger is potty train already?

You can do what my friend did with her three year old. She also missed the time because she had a newborn and it was just too much to do at the time. However, she was well aware that her older daughter was perfectly capable of doing without diapers. So she set a date and she and her daughter started a countdown. When the day came, they threw the remaining diapers away and the girl has been diaper free ever since.