First of all, it has already been pointed out to you that there are ways for people under 4 years to get on the list. I'm not a driver so I don't know the details. You need to read the contract, talk to your union reps, and speak with other drivers.
Second, we are the union. If your local isn't representing you, call them out on it. Go to union meetings and express your concerns. Vote them out. File NLRB complaints. Whatever. You're not powerless.
Third, the responses I saw implied the exact opposite: If you don't like covering that runner's route, work slower. That's the advice I saw in this thread.