History says otherwise
The corporations recruited mainly A level students for Hamble.. criteria was to be 18 when the course was finished. I was one of the older ones at 20.. the youngest retired last year after 46 years flying for BA. Those in their 20s had more problems than the teens. In those days you couldn't get into a major over 26, the exception was Swissair and that was 29 with significant experience. It's about selection and training. In gliding its a function of age to calculate rough solo time. The younger the better.