If the employer's pattern is as clear as you say it is, there may be provable age discrimination. Speak to counsel right away.
This is not formal legal advice.
Massachusetts has an agency MCAD which handles discrimination cases. Changing shifts is very different than not hiring people based on age. Firing employees due to age is very different than hiring younger employees. After working with fellow employees for 13 years you build friendships, so emotions can run high when they lose their jobs, which is why hiring an attorney would be a good idea. You can thoroughly talk about what is going on and find if there is truly a case for discrimination.
The information on this site is not, nor is it intended to be, legal advice. Attorney Satterwhite invites you to call or e-mail for more information, however, visiting his website or contacting him does not establish an attorney-client relationship. Please do not send information that may be considered privileged or confidential prior to establishing an attorney-client relationship.