Am I too young, too inexperienced for an MBA??

Most top programs in the US want you to have work experience before starting, and I'm pretty sure they're open and honest about that preference - even if they don't say they want X years work experience. Some schools are more open to younger applicants than others, but I can't think of any that take a significant number of people straight out of undergrad with no work experience. A lot of this can be explained by the fact that recruiters want MBA graduates to have a few years work experience, so the schools would be taking a risk if they admitted someone without any work experience that the person wouldn't be employable at the end of the program. For example, most jobs I've seen posted want at least 3 years work experience.

As for engineering background, there are certainly a bunch of engineers at bschool, but again most have at least a few years of work experience where they've proven themselves. So again you'd be competing against people who can point to more tangible accomplishments.

My advice if you want an MBA from a US school is to get a job, spend a few years working and taking on increasing responsibilities, look for opportunities to make an impact, then apply later.