Well pending how "mild" his type 2 truly is, his diet may or may not even truly be able to help him that much in his old age.
In all honesty, a lot of cases like this don't turn out so well (my grandfather bit the dust to diabetes a few years ago, it was a very ugly last 2-3 years for him). There's just not a lot you can do to help someone in their old age when they have had diabetes and/or a lack of good physical health for 20+ years out of their youth.
I would suggest getting him to take fish oil and possibly other cardioprotectant/antiinflammatory-type medicines as soon as possible. Possibly a resveratrol supplement, although I cannot attest to this supplement being truly useful for elder type 2 diabetics as the research just isn't far enough, yet. It may be though (much work suggests it is) and at this point he could need all the help he can get.
Get him to exercise if you can, at least extended walks/jogs 5 days a week. The exercise and fish oil will do more than "cutting carbs" ever will. However that's not to say he shouldn't clean his diet out from top to bottom either. No more candy. No more 3 or 4 meals/day. One large meal/day preferably. Tell him it's life or death.
Unfortunately some people probably won't care much though; especially in their old age. Whether that is him or not I don't know. Hopefully he would take your suggestions seriously and try not to make things worse for himself, because that's exactly what will happen. Diabetes is a malicious disorder and it will ravage anyone it can as we are all susceptible to it. Prevention is the best treatment.
By the way I am type 1 for over 20 years, hence I feel at least a little justified in writing a message like this... else I would not do so.