For worms, I apply the between-the-eyes rule to their thickness/fatness instead of how long they are. They don't have much shell compared to other bugs, so as long as you don't go overboard with them he shouldn't get impacted. I gave Wink his first superworms when he was 13", and he did fine with them.
A not on using supers as a staple though- Since they are more fattening and filling than other bugs, juvies shouldn't have more than 15 a day and adults should only hace 30-35 a week. I feed half supers and half crickets for variety, because Dudley gained a lot of weight and wouldn't eat veggies when I used them as a sole staple last year (Not that he is much better about his salads, but it's worth a shot...). So just make sure they don't become too picky and lazy LOL. :wink: