Age 9: It's fun
Age 13: It's fun, and my parents won't buy me any games for my C64 so I have to write my own
Age 24: It's fun, and I can automate all this boring repetitive business stuff to get my work done faster so that I can play more Freecell and Tetris.
Age 26: It's fun, and The Internet just happened and suddenly everybody wants to pay me three times what I'm worth to do it. Woohoo!
Age 31: It's fun, and if I do just one day of it for freelance clients each month I can live on this beach indefinitely.
Age 37: It's fun, and if I put up a credit card form on one of my side projects, people seem to be willing to pay me money every month just to use it.
Age 43: It's fun, and I seem to still be doing it even though I could probably pack it in and live off that SaaS income.
There seems to be a common thread there. I suspect I'll still be doing it in another 10 years.