Yes. Age discrimination is specified in the constitution in a couple places, minimum age for certain elected officials (obviously they should have set a max too )

It is not proscribed by the constitution, so congress can enact laws as it sees fit. You could envision a law that might violate the 14th (equal protections), but everything to date has either been to protect people or for specific job requirements.

The ADEA is the law with the most application, protects those over 40 from discrimination, and applies to all fed, state, local, and private employers except where specific exceptions have been made (we are one of those).

It is also well established (and common sense) that laws or policies restricting youth are OK, for their own protection or the protection of society from their not-fully-developed judgment. Firearm possession/ownership by youth under 21 (or 25) would almost certainly be restricted if not for the 2nd amendment.

However...

A change in the age for reasons of job performance is clearly established as OK.

A change that protects certain, preferred constituents over other constituents would clearly violate the 14th amendment.

You *might* be able to do a phased-in age change (ex. increase it by one month every 2-3 months) to avoid industry disruption. But the elders would sue and argue that it violated the 14th and they might well prevail on that.

But to make age 67 only applicable to youth for reasons of union politics would clearly violate the 14th, unless they could show empirically that younger generations are more healthy and will somehow stay that way for 40+ years.

Best you can hope for is a phased-in approach. But I doubt even that.