They could've gotten away with a mid 20s DG if they didn't make him a whole ass Detective on the force. So figure he goes to live with Bruce at 30 tops and has a 10 year career before dipping putting Bruce at 40ish. Him being gone for a few years is another issue.
Well based on the comics, dikk moved out when he started going to college.... and with this series, dikk always had a beef with how Bruce raised him, so I can understand him not living there for over a decade... it also ties into how Jason Todd took over as his replacement and was rolling with Bruce for some time as well. I mean, just accept it... this is the Dark Knight Returns aging Bruce Wayne here.