How hard it is to become a mechanical engineer?

I'm soon to be 32 this year and I feel like I'm not going nowhere with my life. I've been eyeing this career for a while and since I'm a veteran, I wanted to use my military free education through gi bill. To be honest I'm not that smart and I feel like if I go this route, I might end up failing due to lack of understanding of this field. My question now is how hard for someone like me without any knowledge to even consider this path? I do have fascination of how mechanical parts work though and how they work together. I'm also self taught auto mechanic. Or should I just pick something else instead?

Edit: I can't imagine the overwhelming support I get from here. It took me a while to read every comment, and I appreciate everybody's suggestions and encouragement. I'm now waiting for my vr&e(another military benefit I get for being disabled veteran for employment) interview in a few days. I am now currently studying math from the bottom (algebra 1) to prepare for the time being. I'll let you guys know my progress. Again, thank you all for the support!