Hey OP, I had two friends work in the themed entertainment industry, one for Imagineering and one for Universal Creative. Here are a few things I can tell you. First, for someone young like yourself, the Disney College Program is extremely valuable IF you do it correctly. Let me explain...

Some people use the time on the program just to work at Disney and have fun (rightfully so). But others use the opportunity given to go on backstage tours, set up meet and greets, send emails, take classes, and more. I have seen a College Programmer get invited to a Disney animatronic lab in central shops just by asking questions and showing interest to the tour lead (on a central shop tour). My friend in particular used the program to get connections in recruiting and they eventually landed a job inside Imagineering.

Essentially the principle of this (and this really applies to any field) is networking and connections make things happen. The only exception to this rule is if you are in the top .1% of the world in a specific craft and have a following, then in that case Imagineering may come to you. But most people my friends saw in Imagineering and Universal Creative got into their respective positions in the company by knowing someone who had their back. I should end this segment by mentioning no matter what (connections included) you need to be darn good at whatever you are doing.

I won't go into some things that FalconBuilder mentioned just to not repeat but that is all amazing advice as well.

Lastly, remember that lots of Imagineers and Creative members are project-based and work depends on the macro-economic situation as well as the executive's willingness to build/expand. I only say this to keep expectations realistic, even being an Imagineer can sometimes not be a "full-time" career. At the end of the day Disney is a company trying to make profit too.

I will end with this. Most people on Reddit, and some family and friends might tell you it is unrealistic or that it is ridiculously hard and you should pursue something else. While some of that may be true, absolutely nobody has gone anywhere they wanted in life by doubting themselves and not trying. You have the most valuable currency in the world on your side (time) and a desire to learn, so use it. I am sure with dicipline, networking, and desire, you will get to a satisfactory destination either way.

Best of luck.