My point was really that it's not as straightforward as some people pay less and therefore cost the club money, because the assumption that they would all continue to be members is not reliable.
If 100 were after the £150 reduction, which I think was the original example, that would be a reduction of £15,000 of revenue. If the deal were not given, (assuming fees of £1,000), it would only take 16 of the 100 leaving to make the club worse off. Who knows whether they would or not? That's pie in the sky. But I very much doubt the real cost of the reduction in fees would be £15,000.
You're not strictly correct in your assumption. Some would leave but, to a certain extent, clubs almost operate a revolving door as some return to golf and some take it up for the first time.
Equally, some clubs have retained their high fees and no age related reductions because they're selling a quality product and/or, maybe, selling it the right way, e.g. a reduced fee for all and a pay and play top up.