That is a difficult question. Here's what my situation was at university:
95% of my class came straight out of high school and had no trouble catching up with the (incredibly difficult!!) material. The other 5% (including myself) started university at age 25-27, a lot of us didn't finish high school (went through community college for 2 years) and thus didn't have the awesome comprehensive theoretical background everyone else had.
The statistic sheets of my university showed less than 1% chance of graduating for people like me.. and 70-80% chance for the buttered-up, lucky little high school kids. Well.. I fought really hard, I sought every resource and person possible and finally I made it, I graduated.
For those spoiled high school kids: 15% dropped out in freshman year, 20% dropped out in the second year and 10% dropped out in the final year. From the 500 applicants, about 90 graduated. That's not much eh, you see?
My professor told me: "The actual statistics are: you have on average 8.25% chance of graduating once you set foot in university".
Long story short: If you did really well in high school, your chances of dropping out of college are 10 to 20%.
Mature people are likely to stay and super-determined people like me have to move earth and sun to make it. The only dropout factor here is your maturity, really.. A lot of childish morons didn't have the strength, courage or passion to continue, press on and graduate (these people don't even know those concepts to begin with. They're pampered like babies).
I hope my advice helps!
P.S.: sorry for my lack of vocabulary but I'm rather tired at the moment.
