Summary: David paints a picture of the end of his days, where enemies are still persecuting him. He thinks it is his end, that God has abandoned him because of his sin, but God steps in and serves as his shelter.
Response: I'm not sure if David was actually older when he wrote this, but a less brash and more pensive tone is good evidence toward that notion. Lord, I too have failed again and again. Yet you continue to shelter me and provide for me. Your love really is amazing!