18!!!and not a moment before!!!
my granddaughter's and all the kids in our family started sewing at 4 & 5 years old- not a single one of them was ever allowed anywhere near a rotory cutter before they turned 18---they used scissors just like they use in 4-h or home ec classes!
rotory cutters are razor blades and can easily cut fingers OFF! one of my son's old girl friends (at 22 years old) was in the studio one day working on a project- listening to music- dancing around---ran the rotory cutter off the ruler---to the tune of 57 stitches!!!
when the kids were little they used scissors- and any pressing that needed to be done was done by an adult.
they were taught to use wooden irons- and to finger press- when fabric needed more than that they took it to an adult-
i believe SAFETY should ALWAYS COME FIRST!!! it is no fun when it hurts!
and NO CHILD SHOULD BE ANYWHERE NEAR A ROTORY CUTTER- ANY MORE THAN YOU WOULD LET THEM PLAY WITH A BOX CUTTER- OR ANY OTHER RAZOR BLADE!!!
all the boys in our family are great quilters = very creative- they start right out challenging you - it is great to encourage them- but teach them to use scissors.