Edge of possible: Become more hardworking, competent and charismatic while at uni, make numerous contacts, resolve to actually get something done with my life, and over the course of the next 10-20 years manage to persuade governments and corporations and such to help me get a Verne Gun built.
http://www.kschroeder.com/weblog/the-verne-gun
280,000 tonnes to orbit. That's about three times the USS Enterprise. This is sort of thing that needs to get done, but probably won't, and nobody even seems to be working on it. This is a thing that could be a person's life's work, but (as I sort of implied above) I'm not really driven enough, or competent enough to succeed, so I'm probably going to have to settle for being a normal. An alternative would be thorium reactors, but more people have got that idea in their heads already, and I'm not as passionate as I am about "Space!" and "Nuclear Cannons!"
Actually plausible: To become a successful property developer in the future. That's the least fantastical thing I have that actually counts as a fantasy, things like getting into uni and not failing while I'm at uni are just ordinary plans for the future, they're different and don't count.