It wouldn't be a waste of time if there were not an endemic bias against both having older developers and paying them more for their experience.
As the employer-employee loyalty culture has been systematically destroyed, I am far more likely to see the training of more junior developers as training my own replacement than as improving the capabilities of my team.
If you want me to train someone in anything, you really ought to make me feel secure in my position, such as by offering me some form of job security. For the sake of discussion, let's just call that "tenure". If I am an "at will" employee, the only form of job security at my disposal is to be indispensable, and training others undermines that.
So if your company has a clear career path, with employees from entry-level tenderfoot to ultra-senior guru, and every step in between, you might feel good about training. If, on the other hand, your office is full of young bros, and the dusties are encouraged to move out to pasture when it's time, your time is coming.
If a company truly has a commitment to training, a necessary prerequisite is a commitment to long-term employee retention.