[Gordon Currie]

I think you've already heard a few good tips. Here's a few more:

1. There are two popular approaches to learning how to solo - applying scale patterns and applying arpeggio patterns. Learn BOTH of them. One or the other will only get you so far. Your initial goal is to seamlessly switch between these approaches. Sometimes scalar patterns work better, sometime arpeggios are best, and sometimes you have to mix and match. I've observed most guitarists start with scales, then move on to arpeggios (probably easier that way). Just don't stop until you have them both down cold.

2. At an intermediate or advanced level, you want at least some of your solos to resemble melodies, so you will need to break out of the heretofore useful and benevolent trap of scales + arpeggios. If you sing, bonus. If not, attempt anyway (esp practicing alone). Melody is often defined by its phrasing, and this phrasing aspect is easier to realize when you can sing along with what you are playing. Quickly you will experience solos that 'sing' or flow, and those that resemble a coughing fit (out of control and unpleasant). Realize that it is OK to repeat a note or phrase, and silence or a long held note does not have to mean you failed.

3. The 83 year old you mention has attained something that I'm only recently experiencing after 40+ years of improvisation - fretboard mastery. I find myself looking at the fretboard less and less, yet I can play rapid and intricate lines because I VISUALIZE it in my mind. I attribute it largely to doing steps 1 and 2 for so many years that it finally is becoming natural.

Realize also that there are many paths to improv, and soloing is only one. If you play with others, have them play the chords, and see if you can come up with a compatible accompaniment on the spot. Bonus points if it helps to strengthen the rhythm. Major bonus points if it is compatible with the melody! (This approach really tests your knowledge of the harmonic and melodic aspects of a song, and is REALLY hard to do at first.)

Finally, get ready for YEARS of making 'mistakes' and failing over and over. Even more than general guitar playing, improv REQUIRES you to accept that you are likely to screw up - at ANY level. I happen to think it is worth it, as improv is a skill that a minority have attained.