Becouse it is generally unlawful to discriminate against a person in the workplace on the following grounds. Becouse of your Race
Becouse of your Sex
Your Sexual orientation
Your Age
Your Physical or mental disability
Your Marital status
While your Pregnancy
Your Religion
Your right with most of it but I think the physical or mental disability and age is not. Not about discromination but sad to say, some work won't really fit you with those three. If work requires physical aspects it will be hard to give a quality of work.
For example, being a crane operator while having a parkinson's disease brought by aging. Not just by performance but compromising the safety of other workers and yours.
Again it's not discrimination but being fit for work.