Without knowing more information, it is difficult for me to understand on what basis the employer made this decision. I speculate that in the current job market and economy, the employer may just feel that s/he does not have to pay as much at this time for the work to be done as s/he formerly did when times were booming and good people were scarce.
It could be that there are other skills or knowledge that the more senior typists have regarding the job responsibilities. Regardless, the employer determines what rates s/he wants to pay for work to be done.
Hopefully, s/he uses actual pay market data and treats employees fairly; but this is not always the case. Have you asked the employer why you are being paid so much less than the others? You have told me what it is not (e.g., longevity); but the employer may have a good business reason.
I would want to know how I can earn more; and knowing why I am being paid less would help me determine that.