Even the poorest pensioner is guaranteed an income from the state of over £150 per week. I know that's not much money at all, but the poorest working-age people only get £73 per week from the state, less if they're aged under 25. And they are not exempt from paying for the TV licence.
Pensioners on Guaranteed Pension Credit also get their whole Council Tax bill covered by Council Tax Reduction whereas working-age people have to pay a minimum of 20%.
Pensioners' incomes have been very largely protected from austerity cuts and the £150.50 per year that they are losing now is a lot less than the hundreds that many working families have lost.
I'm sure I read that the subsidy for over 75's is about a quarter of the BBC's entire budget so they would have to substantially cut their output to continue to fund it.
Bearing all this - and many of the comments above - in mind, I think scrapping the freebie is reasonable and I would not donate to replace it.