The grey-haired man whom Paul encounters during the Epilogue describes Jim Gray as Paul's "deputy", but then I guess he would. The Best Year Of Our Lives is, of course, Paul's story, which lends some explanation to this assumption.
Jim is just a little bit younger, and just a little bit smaller, than Paul, and at their age this may indeed count for something. But these slender margins of seniority should not be permitted to obscure the seminal role played by Jim in making this story work. He is at the centre of it all - his father runs the club, his girlfriend is Paul's closest competitor, his brother has an integral role to play and, perhaps most importantly, his sense of perspective more than once keeps Paul treading the straightest path.
CREATING THE CORRECT DYNAMIC
Creating the correct dynamic between Jim and Debbie was one of my most difficult challenges during the writing of this book. Whilst Debbie's oozing charisma and cool bravado threatens to overwhelm all in her path, there always had to be a sense that Jim in some way retains dominance within the relationship. Being older and being male, he can level with Paul in a way that Debbie cannot and one is allowed to feel that to some extent at least Debbie only gets away with what Jim permits her to, for the sake of a quiet existence.
At the same time of course Jim has the added responsibility of keeping his brother Colin in his box, as the latter's more or less similar size and stature enable him to assert a degree of sibling rivalry which defies the age difference between them. Add to that his oft-expressed exasperation with Steve and emotionally Jim is fighting on every front, whilst being the cog at the epicentre of the mechanism which turns the gang sans Paul.
AN ESSENTIAL LINK
Beyond the genuine affection that Paul has for his closest friend, Jim provides an essential link back to the younger members of the gang without which Paul might well have felt estranged. Generally fourteen and fifteen-year-olds aspire to be seen stepping out with the bigger kids, but Paul is able to move in the preferred company of the younger ones because his sidesman, with the slightly younger girlfriend and the still younger sibling, is from his own stable.
Jim Gray is an important, essential component of the complex intersection of personalities which is the Aitston eight. I don't think the story would have retained any credibility without him - indeed I fear Paul would have been left without much kudos and looking a little, well, strange, and set adrift. At the very least, for Jim the right to wear the lumber jacket is one that has been thoroughly earned.