26 is definitely not too old. I started up again at the end of 2003 at the age of 37. The last time I played was in my freshman year of college. I played B-flat soprano and some bass clarinet.
I would suggest getting a plastic clarinet for now. If you need fingering charts, you can use this link:
http://www.wfg.woodwind.org/clarinet/ I used this to re-familiarize myself with the alternate fingerings (one of my weaknesses). The range goes way beyond that of beginner books.
If you need to work on theory:
Harmony and Theory: A Comprehensive Source for All Musicians by Hal Leonard Corp.
I used this to re-familiarize myself with key signatures, chords and scales (besides the major scale)
If you are looking for something other than a beginner`s book:
Tone, Technique and Staccato by Mel Bay Publications
http://www.melbay.com/
It has studies in which alternate fingerings is used in many exercises. It starts with exercises in the lower register to help develop tone then it goes on to crossing the break. This has been helping me with my weakness in alternate fingerings. Further on in the book, it has some Klosé technical studies.
Clarinet Warm-Ups by Kelly Burke (released by Dorn Publications)
http://www.dornpub.com/dornbook.html
This has several long tone and articulation studies. There are 196 (that`s a lot) finger exercises. Some are made specifically for the left or right hand. There and various technical exercises and patterns involving scales and chords. It even has a chapter about physical and mental preparation.
I can even e-mail you some sample pages from these books to see if they are right for you before
you buy them. Please let me know of you are interested.
Hope this helps