Possible Clues:

• Father's bird is over the hill
• Clapped-out old man's one tweeting?
• Decrepit old man's boob
• Getting over the hill, some sherpas titter
• Too old to be of use
• Little bird needing energy to rise over the hill
• Embracing a good man, mine's no longer in his prime
• Getting on by overseeing PC subject?
• Too old, over the hill
• Dad's little bird is too old now