Clue: Understanding where population's 50+? (8)
Answer: SAGACITY
Explanation: Definition: Understanding
My first thought on reading the clue was that the answer was SAGACITY, with a play on SAG; I promptly dismissed this and hoped to find something better. It turns out that I had the right answer for the wrong reason: from somewhere I dragged up Saga Travel (not any reflection on their prominence, just on the time I have been out of the UK). Although their website makes minimal reference to age, Wikipedia does give as a British company focused on serving the needs of those aged 50 and over.