It's when you are 6 foot under.
One thing keeps recurring when I speak with successful business people. All of them, with the exception of none, are constantly seeking and soaking up new information. They are constantly learning.
Whether it's reading, watching online videos, attending seminars, they tend to have this constant hankering to soak up knowledge to get the next idea or to improve what they are doing. Siimon Reynolds rennovated one of his homes around his books so as when you walked in the hallway central wall itself was a double sided bookcase.
And it's not about MBAs, many don't rely on formal education but rather constant learning. They also step outside of their familiar worlds and get input from different walks of life and business.
Another commonalitiy is that they seek mentors. People who can guide and teach them, and they seek to also mentor others.
So today, ask what are you learning? what are you reading? who are you learning from? It never stops.