If it is about something specific, how about taking him out for a meal and talking to him in a thoroughly grown up way - 'man to man', so to speak. For longer term guidance, I guess you need to establish a mutual respect, perhaps asking him for advice on something first?
Wow, that's a toughie. Do you have a mutual interest in a sport or subject on which to try to build some rapport. Does he actually want guidance? Or does he bottle up and try to muddle his way thro'. Sounds like he maybe following Dad and Granp and finding it difficult to ask for help. Good luck with this one.