I don’t agree that this is necessarily a weakness or that it’s overly strange.
While they might not be able to quite hit the peak fitness of someone in their 20’s and 30’s, you also gain a large amount of meaningful mental fortitude as you get older.
In short you have seen more shit and dealt with more shit. So generally you can bear more headship and pain before breaking, also probably less prone to discipline issues, and the older ones likely provide a good example to the rest.
In a war for the survival of your nation all able bodied people are needed. There are naturally more older people than there are younger ones.
Pretty positive this is going to end up being a DNS level block that will be as simple as setting a dns server outside of the UK to bypass.
Because anything else would create an unbelievable amount of administrative overhead.
Also imagine the spike in identity theft this is going to cause.