In ye olden days of yore, there was a problem with synthetics seeming to cause built up varnishes on inside surfaces to flake off as particulates, contaminating the oil, etc. Today's non-synthetics are greatly improved (and synthetics almost always have dino stock base) so this is not realistically a problem before 100K miles...if then. If one is worried, a 1,000-mile Amsoil engine flush can be used as a transitional step.

And if he doesn't change, it will matter little as long as he's maintaining regular oil changes. Modern dino oils are excellent. I ran my previous turbo Volvos to 275K and 165K miles on dino...and sold them for good money. They were in great shape with free-spinning turbos, full compression, and infinitesimal valve train wear.

So sleep well tonight.
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David (98 S70 T5SE Black, misc mods (mostly lighting), red calipers) (92 940GLE)

Well you can tell your dad that Volvo actually recommends (in my owners manual) synthetic oil for my 2002 V70 when: you are towing a trailer, do alot of mountain driving or stop and go traffic. i.e. severe duty maintenance schedule. so perhaps this will give him a vote of confidence.
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You will never leave where you are until you decide where you would rather be - 2002 V70 stk, /w /tinted windows

Simple. People don't like change, especially if they don't understand it.