T&B et al
BALPA is not trying to stop you flying at age 60, what it is trying to do is to improve safety in the industry (the onshore branch of which could be said to have a relatively poor record of late) by encouraging operations to switch to 2 pilot (safer and creates more jobs), and by recognising that, despite all the age discrimination legislation you can muster, the probability of sudden incapacitation does unfortunately increase as one gets older.
You can of course argue that the cut-off age should be variable according to the individual. This is true but impossible to work out in advance in practice. Some say "I can pass a medical and an OPC so I should be able to continue" but realists know many die or become incapacitated with a current medical, and OPCs are typically so formulaic that an old hand can pass one with eyes closed, regardless of deteriorating real ability.
Whilst it might suit your personal agenda to carry on flying single pilot until you croak in the cockpit and kill your passengers, BALPA considers that this is not good for the wider industry!
HC