Read Lost Arra's post. Over and over, especially the part about getting in shape! Not meant to scare you - but the better shape you are in the more you will enjoy your time in the mountains.
As far as guided versus unguided goes, there are pluses and minuses to both. If money is not a big issue, and you can hook up with the right guide you will learn a bunch in your first trip. And that can shorten your learning curve. But if you have to put off the trip a few years to save the money for it, I would say forget it and just go now! As you said, we're not getting any younger, and I sure wish I had started earlier.
Read all that you can find, through posts here, books, magazines, etc. Spend countless hours on the internet searching states and areas you might be interested in. Buy the Elknut DVD's for a crash course in elk hunting from one of the most knowledgable and successful elk hunters around. The Primos Truth Series elk hunting videos are also well done and informative.
Last, but not least, be prepared for an addiction to take ahold of you like nothing else you have ever experienced! Elk hunting is not for everyone, but it is also like no other hunting I have ever done!