Are braking vibrations a sign of the end of the life of a wheel?
Is there any kind of wobble or unevenness in the rim? There shouldn’t be more than about 1mm of wobble. If there is a noticeable wobble the wheel might simply need truing.

Are the brake pads properly aligned? They should wear evenly over the whole surface.

You can measure rim wall thickness with a caliper gauge. A sign for rim wear is also if you can measure a deformation (change in rim width) between zero and maximum tire pressure.