Arm workouts for age 74 and up...question about best technique for growth in size, not so much strength

I have been working out for a long time but my arms are my "lagging" body part.  I'm tall, 6'1" and my muscle attachment is not at the elbow joint but a couple of inches above on the upper arm.  I read somewhere that this means that I can't get the mass that those with attachments right at the elbow can get because of poor mechanics of the arm muscle.  Is this so?

Using a variety of different techniques and angles, emphasizing expanded, contracted and midrange, with different pronations of the wrist, high reps (like Charles Poliquin's 100s), low reps with heavy weights, everything in between..., I have built up some size compared to before, but nowhere near what the younger guys (with the right muscle attachment?) have achieved even though I've been working out for years before many of them were born! I'd love to have Mike McErlane's arms!  What do I have to do to break through to really huge arms?  I work biceps and triceps equally, of course.

Thanks for the tips!

John