Possible Clues:

• By the sound of it, just look at 30 across of old
• By the sound of it, view the old river
• Showing the failings of old age
• 17 across was not to look over the old river by sound
• Take a look at about nothing so old and gaga
• Just take a look at the ancient river
• Lacking marbles?
• Suffering from mental weakness due to old age
• Suffering from weaknesses of old age
• By the sound of it, take a look at Old Man River? (6)