Depends on definitions of older and younger, however a young family trying to save up enough to buy a hours while raising 2 kids has many more expenses than a 55 year old at the peek of their career with their children left the nest. On that ground it is reasonable to have differing tax rates. However, I believe there are better ways of achieving this than purely age., because what if you are a 55 year old starting a new family and desperately trying to make ends, etc.
Increase the tax free allowance to 18K. Increase the deductions for dependents/children. Allow some part of rent to be tax deductible. Increase all tax bands by 2-3%. Add a 0.5% wealth tax on capital over 100K.
This way everyone can share the same benefits regardless of age.