Sell your Gran on ebay!
I have the exact same problem but I m 15! I do housework for my grandad every fortnight. It brings a few pennies in. Try asking family and neighbours if they want their car washing for a fiver. You could sell some bits that you don t want at a car boot sale...good luck!
Everyday, knock on your neighbours doors asking for odd jobs. By returning each day, they have a chance to think about it. Good luck.
You could start a completely free home based online business.