This is the question :) Sounds funny enough however for me this question is at the same level with the one about "best time to start". Entrepreneur should simply be or become. That's it!
Regardless the motivational things and related to it you have probably already came across the info-graphics about entrepreneurs that have built fantastic companies and they started with only 1 idea and were able to change the world. Yes! starting from one-self. That is important. For some people entrepreneur life begins quote early at 20-s and for some after 40. This is so individual! For some people it's inspiration and for some it's experience!
Have a look an the infographics below from Entrepreneur:
Following your intuition and inspiration should be the best advice. If you have an idea then go and implement it! This is the best thing to start with and you learn every single step. Many entrepreneurs gather experience first and when they feel that's the right step to take they just go for it. Feeling confident that you are doing what you want to is one of the signs to follow. Stop waiting for the best time. If you are looking for the best day to start you know already that this day will never come.
Saying that, here you have an interview with Eric, one of the youngest world entrepreneurs who follows his ideas and dream, finds like minded people who can support him and gets things done! That's the way to go. If your time to become entrepreneur is 11, just do it! If it's 37, go for it!