Never did get many tips when I was delivering even when I started as the "helper". Mostly from older women.
Don't get no ideas when I say older I mean like senior citizen old. the tips dried up for myself after my Uncle retired but that was expected and I really wasn't expecting them at that point anyway
My suggestion would be if you have some young guy doing all the work you might want to consider tipping him, probably not making much at all and he'll certainly appreciate it. Be sure to not let the owner know it. I never took tips from anyone that worked for me and would even give them my tip if we both got tipped but I've known some who would take half.