Rates are decent at the moment, so a 10-15 year fixed term annuity looks as if it could be a good bridge to pension age. But the info I've found so far only talks about buying an annuity with your pension pot, and therefore at a minimum age of 55.
For fixed term rather than lifetime, it shouldn't matter to the calculations what age I am. So is it possible - can you get one earlier (with money held outside a pension)?