How hard is it for my employer to increase my holiday allowance?

I asked my boss nearly 10 months ago if he would consider giving me an increase in holiday allowance as I have been at the company nearly 8 years and have no sick days and impeccable time keeping. At first he seemed keen on the idea, but I have repeatedly reminded him every couple of months hoping he will sort something out. He now tells me he can't do it as from a legal point of view it could be seen as discrimination against people that are younger than me. Is he speaking the truth, or as I suspect, treating me like a chump?