We are investigating possible triggering scenarios which may give rise to powerful jetted active galaxies such as classical double radio galaxies. Important clues come from studying those objects which have most recently been triggered. The newly discovered 'Youth-Redshift Degeneracy' for classical double radio galaxies means that the highest redshift objects in a flux-limited survey will be observed to be significantly younger (more recently triggered) than the more nearby objects. We are pursuing this investigation with a new sample specially filtered to favour the detection of high-redshift radio galaxies. We will present some preliminary results of a near-IR imaging campaign using the UIFTI on the UKIRT.