65K miles is nothing on a 4Runner. You're question.. You've never bought a used vehicle?
Very safe to buy a used vehicle. Take is to a local mechanic for inspection before buying. Check the VIN on Carfax.
Generally speaking Lineman is right on this. 65K on a 4Runner SHOULD be insignificant, but it all depends on how the previous owner(s) treated it. You can't just make a blanket statement that it's safe to buy a used vehicle. It all depends on how well the truck was taken care of. It is totally possible that a truck well maintained with 165K miles on it could be a better buy and serve you better in the long run (and be more reliable) than one with only 65K that has not been taken care of.
I would definitely check with Carfax as Lineman suggested. Keep in mind that a Carfax report is only as good as as the information reported to it. Equally important is ask the owner for all maintenance and (if any) repair records too. If they can show you everything documented in writing going back to when the truck was new, that's a very good sign it was well taken care of AND it proves they had each service done and when.
If they can't show all the records, you just don't know......the very fist oil change could have been at 30K miles. Also, during the very critical first 1000 miles, it's super important that the truck was driven very very gently, like a grandmother would drive it to properly break in the engine. This will be difficult to find out, but if a teen driver for example, had it when new, I'd be careful.
Again, as Lineman said, get a good mechanic (chosen by you, not the seller) to look at it and that should tell you volumes about how well it has (or has not) been maintained.
You can also tell a whole lot about how well the truck has been maintained simply by looking at it. Does that paint still look good? How do the seats and carpets and floor mats look? Are the tires wearing evenly, or does it look like they have never been rotated? Chances are that if the seller has not taken care of keeping the paint and interior in good shape, he definitely has not bothered to take care of the engine and drive train either.
Just my .02 cents. Hope it helps.