Estar entrado en años / Pintar canas / Andar rondando el hoyo

Click on the image to watch the video of the song, «Over the hill» by Monika

Meaning:

Too old to be able to do something; to escape  from prison or the military.

Click on the image to listen to the symphony «Over the Hill» by Antonio Seixa

Origin:

If we considered that the lives of humans were like climbing a hill or mountain; then, we would have to say that when we are born, we are at the skirts of the hill. As we grow older, we scale on the slope up to higher areas. When we are at an old edge and very close to arrive at the end of our lives, we would be on the hill. If we are over the hill, it is because we are living more a longer life than the rest of people. On the other hand, for the second use of this idiom, we have to remember that prisons and the military are usually built at far and away areas usually surrounded by hills and mountains so that not everybody can trespass into their facilities or escape.

Click on the image to learn more about this idiom with BLT Eigo

Example: