joelsnan however many younger immigrants you have or don't have, it does not alter the basic fact that at the moment, year on year, there are more elderly people needing more care. However many younger people there are, the raw number of older people is climbing quite rapidly.
Even if we had a perfect system for discharging people from hospital (and I agree we are a long, long way from that) there would still be more people every year having cancer, having falls, having pneumonia etc. Therefore demand at the front door of an NHS hospital will get bigger than the year before, every year, for the next few decades, and then stay high for about another decade or so, before it starts to decline a bit.
Immigration helps the NHS because we need more young working people paying taxes to pay for all this healthcare.