Kids take a lot of time, granted. But grad school? It takes 4-5 years (1), and during that time, you can work on your startup part time. You also develop technical skills, which you can later use to work outside the (somewhat crowded) webapp space.

(1) The average is 6 years, but that includes lots of lazy people, future college teachers, people who enjoy grad school, etc. Potential startup founders would almost certainly be faster.