I say stick to 54/80 for 13 year olds. My son who will 14 soon has pitched both - at 60' it takes more effort and feels likes he's thrown enough at 60-65 pitches while at 54' he usually throws 85-90 pitches. So 54' is better for development (more pitches thrown) and kids have a shot at throwing complete 7 inning games.
Also, at 54' 13 year old's fastballs can be effective. Throw the same fastball at 60' and unless the pitcher throws extremely hard for his age it just won't be effective as a fastball. This then makes the pitchers throw a lot more "junk" and they don't develop the fastball as well as they should be.