Charles H. Spurgeon on Psalms 71:9

Cast me not off in the time of old age, etc.; for now I have most need of thee. The white rose is soonest cankered; so is the white head soonest corrupted. Saepe nigrum cor est, caput album. Satan maketh a prey of old Solomon, Asa, Lot, others; whom when young he could never so deceive. The heathens, therefore, well warn us to look well to our old age, as that which cometh not alone, but is infested with many diseases, both of body and mind. This David knew, and, therefore, prayed as here: Cast me not off in the time of old age; forsake me not when my strength faileth. He is a rare old man that can say with Caleb (Jos 14:10,14), "Behold, the Lord hath kept me alive, "etc. John Trapp.