Intuitively, we all know that our metabolism slows as we age. Did you though this has been quantified? Here’s the chart of Basal Metabolic Rates in men and women vs age:
So this, at least in part, demonstrates why it is harder at 50 to lose weight than when we are 20. For a man of 20 their BMR is about 46 and the same man (at the same size) their BMR is around 38. That’s only 82% of the age at 20. So, yes, it is harder to lose weight since you have to eat less to lose weight than you did when you were young, but it is not at all impossible.
Even if you are older, you can do it.