> I told my wife that it was very possible that we would be millionaires by the time we hit 40.

Are you being colloquial?

Being a millionaire by 40 (in 7 years or less) is quite likely for anyone with the talent to launch a startup, by working at a regular big conpany.

Launching a startup lowers those odds by quite a bit (but increases the small chance of being a manymillionaire).