Hola eltorero! EF's Grand Tour of Spain looks great - the itinerary is much more interesting than most that you'll find. And EF's prices sure are hard to beat!
I can really understand where you're coming from! I organize multigenerational tours and I think they're wonderful. My son, who must be about your age (starting university this fall) is also a great fan. It sounds to me from this and other posts like the two of you have a lot in common!
Here's a bit of advice. If you're set on going again with EF, try talking to the teacher in charge of the trip at your old school. Ask if they would consider taking you along. Numbers are important on these trips, and the teacher in charge may bend rules to add another person who isn't a student. Really. Try it. That's probably the only way you'll go on a tour with EF, unless you can convince a teacher you can be a chaperone!
It's very hard to find another tour with prices as low as the student companies like EF offer, and of them all, EF is one of the cheapest. As far as the tour guides/managers/directors go, these great people tend to freelance and work for any number of companies. Europe is filled with great guides, and they're the ones who make a tour a success. Luckily, they work for lots of companies.
The other thing that will be hard is finding as good/complete a tour with another company. Most tours of Spain are shorter and hit the main sights only - Madrid, Seville, Granada. Maybe Toldeo, Barcelona, Cordoba. Costa del Sol is often thrown in for the beach. (There are cheap hotels there, and plenty of them, which is a concern for big tour operators. Otherwise, IMHO there are MANY other more attractive beaches to visit in Spain!) I took a quick look around and here are some links for you to take a look at.
This one has lists of tours to Spain from many companies. It'll give you an idea of what's available and the names of the major tour operators.
http://www.tourvacationstogo.com/spain_tours.cfm Trafalgar\'s 16 day Best of Spain tour looks like it may be your best bet itinerary-wise, and Trafalgar is excellent. They hire only the best tour managers.
Another one is Gate1's 17 Day Iberian Kaleidoscope
http://www.gate1travel.com/spain-travel/17D-iberian-kaleidoscope.asp You don't have to be part of an organized group to go on these tours. You would travel with whomever else signs up. You could end up making great new friends!
Of course, you could also travel on your own. It's a bit daunting, though, if you've never done it before, and somewhat limiting if you have to rely on public transportation (although it is very good). Personally, I love traveling with a tour manager and local guides, because I learn so much more with them, and I enjoy traveling with a bunch of people. I also like not having to worry about catching the train or bus when I don't know where the station is, or wondering where I'll sleep! The guides also know the best places to eat and things to do. They're a hundred times better than a book! And to think I traveled on my own for years and years...
Good luck!