Now is the time to start. I usually banded my Cockatiels between 6 and 10 days of age (depending on their size).
I used to have a great link with pictures and everything on how to band, but I've lost it. This may help though if you've never banded before
Click~HereBecause of their age, they may be too old for banding. If you have any difficulties getting the band over the foot, please don't push it. A little wiggling is okay, but don't force the band on.