chicks big adventure

We've been putting our 5wk old chicks in a secure run for a few hours each day when it's been sunny and they've loved being outside. It also gave the older girls a chance to get used to them. This evening we thought we'd let them have the run of the garden with the others and the older ones totally ignored them! They spent most of the time following us around and much to our surprise and pleasure 2 of them flew up onto our shoulders and sat there like parrots! We were chuffed to bits as our older girls have never done anything like that. They're obviously going to be very friendly birds but I think a bit of wing clipping is going to be necessary. Can anyone tell me the best age to do this?