Stalemate.....unless Goku is dumb enough to get in close combat with him then he gets ripped in half.
Stalemate, even if Goku get's close he can dodge every punch Juggernaut throws. Nothing Goku does will scratch Juggernaut
Old age? Are we really talking about that? You know Goku also has an extended lifespan thanks to Elder Kai, who gave him 1000 years extra, plus as a Saiyan Goku has retarded aging as well, the upper limit of which is unknown. Also unlike Juggy he can return in Spirit form. Can't believe we are talking about old age. Limitless possibilities could happen in that time. As for the genki dama, since Juggy is evil it probably could harm him, but still I doubt it would kill him, so no i don't think it would work.
lol Goku was like 60 by the end of DBZ and looked like he did when he was 19 only with more muscle. Saiyans aging process is severly retarded, it's almost like they don't age past a certain point, I can only imagine how old vegeta's dad was, he looked like 40 or so, so I imagine he was easily 100+
Favoring Juggernaut. You can tweak the battle conditions to ensure Goku stays SSJ3. But fact of the matter is Goku still has limitations on how long he can fight before exhausting all his ki reserves. Juggernaut has no such limitations for his energy thanks to his link to Cytorak. Goku may have advantage in flight and speed, but he doesn't have the means to kill off Juggs. BFRing Juggy by Shunkan Idou (IT) won't help Goku out either as Juggernaut has the ability to open up portals that allow him access to any location in the known universe. Pretty much, Goku dies when either he is dumb enough to get in melee range of Juggernaut or he exhausts all his ki reserves in failing to halt Juggs and gets left to the mercy of the big guy.