I don't think there is a free list anywhere of what skills are required for each JO level. You can buy the information from the USAG website if you are interested. I bought the DVD with the Levels 1-6 routines and they are very helpful. I can tell you that you have to be 6 to compete Level 4 and 7 to compete Level 5, but as gymnastmomof4 mentioned, there is no other age limitation. The girls compete within age groups in their level. My DD's level 4 group has girls ranging from age 5 to age 9. Level 4 skills include:
Handstand to forward roll
Handstand to bridge, kickover
straight armed backward roll to pushup position
round off/back handspring
various leaps, turns, splits
In addition, the girls on our Level 4 team can do front and back limbers, front and back walkovers, some can do front handsprings, front and back tucks on tramp or tumbletrak.
front hip circle
cast to shoot through, mill circle
back hip circle, underswing dismount
They are also working on kips and cast handstands, though none of them have these skills yet.
handstand on beam
side handstand hold to quarter turn dismount
split leap, tuck jump, straight jump
half turns and pivot turns
The vault is a run, hurdle, jump to handstand fall to flat on back on stacked mats.
Level 5 adds a front handspring on floor, ro/double back handsprings, back extension roll to handstand, plus a full turn and the dance gets more complicated. There is the addition of a cartwheel on the beam plus a full turn. On bars, they need to be able to kip as well as cast to squat on, jump to high bar, tap swings. The vault is a front handspring over the vaulting table. Level 5 girls are also working on cast handstands on bars, back walkovers on beam. The Level 5 team has girls from age 6 to age 11. I hope this helps a little! It sounds like you are in rec classes. I would ask around at the gym about how to advance to team if your daughters are interested.