Which makes perfect sense, if you have an ounce of common sense. If you ever visited a hospital (a hospital for adults, not a children's hospital) in your life then you will have noticed that the average age there is far higher than that of the general population. Old people have worse health - which really is the most obvious thing in the world.
Now, most immigrants, anywhere ever, are not old people. The majority are healthy young people, again, obviously. It's not Polish pensioners that flooded the UK.