Tbh no, almost all driving jobs are 21+ for insurance reasons. For many companies the extra costs trying to insure younger/higher risk drivers are just not worth it, and even if self employed the 'Hire & Reward' insurers pretty much all have the same 21+ rule. You also need to have been driving for 2+ years for many of these role, even besides age.
One big reason for a lot of of this is that delivery vehicles are often pretty expensive and harder to drive. It's hard enough trying to get insurance for a £5k Corsa at 18 let alone a £50k odd delivery van.