It becomes diminishingly difficult to go back to school as you get older. The same applies for doing a startup, unfortunately. The difference is that you can generate income while building a startup. It's more difficult to get investors to pay you to go to college. Thus, finish.
To make your task easier, here's my rule-of-thumb formula for determining the difficulty level for finishing college or creating a startup:
(log(m+1) + w^2 + c + s) x log(y+1), where m is any mortgage, in dollars, w is the number of wives, c is the number of children, s is yourself, and y is your age, in years.
To give you an idea: the average 20 year old has a difficulty factor of about 1.3. A 30 year old with a family and a mortgage is about 6 and a 40 year old in the same boat is about 15. YMMV.
Good luck.