It is cultural thing, you know two countries separated by a common language.
I think he (although it could be a she and I shouldn't presume) is trying to be complimentary here - around the block could infer experience rather than merely age.
Anyway, if you are happy being on your feet for 50 miles train over shorter distances because, as has been noted previously, recovery is quicker and damage to muscles & joints is less. If, however, you are not sure about eating and drinking 'on the go' or you are not sure your shoes/socks will be OK for 50 miles then maybe you need to practise at or close to that distance.
Don't forget to carry anti-inflamatories, consider taking them after 25-30 miles so that if/when you need them they are in your blood already. Carry compeeds and maybe a pin for bursting blisters and perhaps zinc oxide tape for your feet.
May also be worth a look at
http://www.ldwa.org.uk/ and the 'Discussion Forum' (link on front page) where there is advice on blisters, feet balms and all sorts of other black magic to help survive long distances.