Try get him to sit down with you and watch some videos like the WEED series by Dr. Sanjay Gupta.
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When you do, have a joint of some nice, smooth, low flavour, high cbd, low thc bud hiding in your pocket.. because if you manage to get him to start watching the series, at a certain point, he could have a fleeting thought of possibly wanting to try it, and if you have everything ready to take the opportunity right then and there, and you give him a pleasurable first time experience smoking a joint, I think that would give you the highest chance of getting him to come around.
I think a joint of straight blue dream would knock his socks off and either put him to sleep or risk giving him a bad experience. If that's all you can give him, only offer one toke, and if he says he doesn't want any more definitely don't insist. If you insist, then that extra toke makes him too high, he'll probably never try it again. When it's your first time 1 toke is like 1 joint for a stoner. I don't know what your smoking habits are like but I think when we start to smoke every day it's easy to forget just how low our tolerance was when we first started. Every time I come off a tolerance break of any nature I need to have only 1 or 2 hits at a time or it's less enjoyable.
Maybe if you made some really weak edibles or a glycerine tincture to use sublingually that could be a nice introduction to the feeling of being high too if he's too averse to smoking things. Salves can be easily made with coconut oil and beeswax and have the highest likelihood of getting even the most uptight elder to try the "devil's weed". After they feel the pain relief of topical application it might uncloud their view of our much loved plant and open up their mind to try the other things mentioned.