He’s younger than my own children. Nothing “to it”, other than we get on well, and have similar interests. He’s very “nervous” about going places alone. I’m not. I’ll happily travel and go to concerts/ theatre/ events/ holiday alone. There’s a show in London that we both want to go to. Would I BU to invite him to come with me. No overnight stay. We know each other through work, and I wouldn’t want anything misconstrued, by anyone, including family members. (We know each others family). He’s an adult, (under 21) and can make his own choices so it feels weird to approach his parents first.
YABU - go on your own
YANBU - ask him if he wants to join you