Mine came along with me from 14. CSM made pragmatic decision that he couldn't be left by himself so he could join us at our "safe" location as long as he stayed in the area where we were standing (and where the public also were allowed).  He had to stay where he was if we had anything to do or "help" from the safe area.  Worked well for us and he got a good insight into what to do.  At 19 he's a real old hand now.  He was really good for going to the cars to get us brews and butties and so on.  Once I crossed the fence to ride in the event he continued to do the practices and the races I wasn't in, but only from Governors to the Pits.  I had no ride this year so we went to separate places on the Mountain for practice week but on pit duty for race week.  I'm not sure I'd go anywhere other than the Mountain now.  Loved it up there.