Millennials are the offspring of baby boomers. Do not look at them as your replacements. Respect their fresh perspective as a tool to make your task easier. Respect their position, avoid attempting to parent them regardless of what you may perceive as a defect or lack of experience. If you must train them, use it to your advantage make your life easier, and check your ego at the door. If you have one foot out to retirement please leave on good terms. In the event, the promotion was due to ageism you may or may not have a case.
Avoid confrontation pick your battles wisely if at all. Unless it is a strong union shop and you have tenure, in most cases human resources will side with the supervisor.
An hourly salaried employee with overtime and benefits in some cases earn more than the entry-level millennial's supervisor; especially, in the automotive and manufacturing industry of unionized shops. Salaried and hourly employees are quite different. If a salaried millennial is hired with extensive experience and credentials, many can command higher salaries and benefits that far exceed the employees of their business unit.
If you find yourself having a hard time adjusting, ask the following questions? Honestly, evaluate why they are your supervisor?
Conduct a self-evaluation?
Did you keep up with technology and current practices?
Did you take advantage of tuition reimbursement and training opportunities offered by your employer?
Did you seek additional education and training outside of work?
If you were “grandfathered” into a position but, did not obtain the new credentials in a timely manner, who is to blame?
Did you rely on tenure and not tenacity and skill for the opportunity?
Were you hoping the “good old boy network” would work in your favor?
Where you an asset or liability as a worker? Would you put in the overtime or utilize every sick day just because you had them?
Has your work ethic changed that would disqualify you for promotions?
In retrospect, some things are just out of your control. The company may be changing directions and your expertise, although respected, is no longer needed. You may need to have your plan B ready. Production demands and more flexibility may have caused the surge for younger managers and supervisors. Cost is also a huge factor as a new supervisor needing grooming cost less than a seasoned veteran at the top of their pay scale.
The worst denial of all would be nepotism regardless of how hard you try there will always be an heir to the throne.
There is a happy medium when the seasoned workers and the millennial's cross and that is during the childbearing years and the pre-retirement years. Spikes in health costs occur during these spikes for both groups. However, during these spikes, many of the seasoned lead employees continue to perform as they always have without the added responsibility of a business unit.