The prerequisites for the PE vary from state to state in the US, though they generally follow the recommendations of the NCEES. As it happens, I know someone with a PE who doesn't even have a four year degree. More than anything else, the key to taking the Principles and Practices exam, is documented working experience.
These days, you probably will need the four year degree, and proof of passing the EIT exam. Then you document a certain number of years working as an engineer with someone who holds a PE. Some states also require the co-signature of several other PE certificate holders to say that you're a decent and moral person.
Many states, such as Maryland, allow for alternative demonstrations of experience for those with lengthy military backgrounds. This experience exception is for cases where the ultimate design products are classified.
As for me, I took the PE without needing the EIT because I documented 15 years of solid experience working with other PE certificate holders. Some states allow for this, others may not. My employer places a premium on such certification, and they make sure that you have plenty of opportunity to earn one.
All that said, I must emphasize what the PE is, and what the PE is not. The PE does not indicate that the design is any better or worse than a design coming from someone who doesn't have a PE. It is merely a statement of liability. You can certify the work of others if you know it to be safe, reasonable, and ethical. However, if you design a bridge, and it falls down due to a fault in the design you certified, you and your successors in the company will be personally liable for the failure of that bridge. In other words, you are signing your name to a design that you are certain is reasonable and as safe as it can be.
A PE is also an indicator of expertise to a court of law. In matters of engineering, a PE is generally expected if you are to testify as an expert witness or filing a brief as a friend of the court.
However, as a practical matter, having the design stamped by a PE does not mean it is any good. I have seen drawings stamped by numerous PE certificate holders that wasn't worth the paper it was drawn on. The design got built anyway, and though it is fail safe, there are numerous flaws and failures in this design that make the ultimate product a massive waste of money. Incidentally, the firm that perpetrated that design has earned a permanent place on my personal black-list. I will recuse myself in any future work with them, primarily because I can not be objective with them, and also because I don't trust their work enough to allow my reputation to be associated with anything they do.
Basically, that's what the PE is about: it's about your reputation and your stature as an engineer. It is an indicator of professional responsibility and ethics. It is not an indicator of competence.
