Airport Extreme Red Light

I don't know the model.

Does the AirPort look like a white tower.....about 8-9 inches tall?........or........does the AirPort look like a small white pizza box?

IF.......the AirPort looks like a small white pizza box......look on the bottom of the device for the model number. It is usually embedded in the foam pad base.......starts with an "A" followed by 4 numbers.

IF.......the airPort looks like a white tower........just say that you have the "tower" model.

In either case, routers designed for home use have an average useful life of about 5 years, so an AirPort purchased in 2016 should go into 2021, possibly longer.

Assuming it is Gen6 tower model you can pull more info from the airport utility. It will at least tell you if the fan is running or not.

https://discussions.apple.com/thread/7441098?answerId=32262252022#32262252022

I would suggest you power it off overnight and see how long it takes for the overheat message to appear.

If it appears almost immediately after power on the sensor is faulty. It happens often.

Does the fan roar as overheat condition should send the fan speed to >5000rpm?

Which exact model is your AirPort Extreme base station? Regardless, at this point, you should stop operating it to prevent any further damage to it. If it's the "tower" style unit, you should see vents on the bottom. Be sure that they are clear of any dust or debris as these can reduce the airflow into the unit. Also as Rudegar has pointed out, it may be possible that the base station's cooling fan has become clogged or even failed.

maybe the internal fan broke ?