Agreed... obvi. you aren't gonna do a C4D or even a poser all by yourself. Heck even the poser guys licensed a lot of their tools from 3rd parties. But that doesn't mean you can't do cool little apps that rock at some feature. This is exactly how apps like ZBrush, 3DCoat, Silo, VRay etc got started. And after it becomes popular, then you find some investors (or con your family/friends) and get a team together to improve and expand the tool. Soon you've got a bunch of customers and are rolling in money. Well ok, you probably aren't, but you can certainly make a healthy profit while doing something you enjoy. With a bit of luck, after a few versions you catch the all seeing eye of Autodesk and they buy you out for a bajillion dollars. Now you can retire to a private island and fill it with real basketball boobie chicks :D

As for how long it takes, i'll say this again, more then a language, you need to learn math. Languages are easy, anyone with half a brain can learn C/C++ in 6 months. Sure, you wont be a master but you can learn enough to make whatever programs you need to. The hard part is having a good understanding of vectors, matrices, geometry, trigonometry, a bit of calculus and how to use numerical methods. You will also need excellent management and organization skills, because 3d apps are a nightmare of complexity. If you can become/are good at these, then you can make 3d stuff pretty fast.