If he was born in 2150, he is minus 132. Z
Also, only 14 years before another Nuclear war in the Dredd-verse 
When Britain gets nuked so hard that Brit Cit disappears and all pre-Megacity towns grow back again.
Actually, Brit-cit does appear in at least one SD story, but not more than 3 I think*. But, yes, the other UK cities (Milton-Keynes, anyway) seem to have returned.
*I forget precisely which one(s), but I believe it was either a reboot or back-flash stories though. If the former, then the canon is perhaps subjective. A bit of retcontinuity, either way. I kind of like the idea of Brit-cit being a constant in different strips. A lynchpin for geek/nerd types like us to to speculate about. That’s not to say I think Dredd, Robo-Hunter and SD actually share a continuity, although the first and last sometimes do.**
**I like Jim’s idea that Dredd is part of SD’s history, but SD is not necessarily in Dredd’s future.