Most of the times also to start up something is when you have actually gotten enough knowledge about the business and your involvment and operations in the business would give you the needed experience in the business.Most people wait till they are close to retirement or when they have excess funds before they start thinking about starting a business. The following are the times I believe is best for anyone to start a business.
1. When you are young.
2.when you have no responsibility
3.when you don't find pleasure in working for others.
4.when you have an incurable obsession. Etc
Feel free to add yours.