they are the best made hybrid cars and they can last quite some time but personally I would not buy one that's more than 12 years old and has more than 100,000 miles on it

The Priuses may be good for up to 150,000-200,000 miles (give or take) before very expensive repairs are needed (battery replacement, hybrid system repair).  Also, it will be hard to find a competent mechanic that knows how to work on hybrids and being a speciality it will be expensive;  going to the dealer would be bad as well.  I would just re-consider and get a normal gas car.

https://m.youtube.com/watch?v=p0F5e-lrlWQ

I would agree with Scotty. I'd also get the newest and lowest mileage model that fits your budget. You don't want to have a battery replacement soon after purchase.

This is just anecdotal observations from lurking in Prius forums for the last decade or so. 

It seems that the battery and hybrid drive train on high mileage younger Priuses last just as long, if not longer, than older, lower mileage Priuses. What does this mean?

I wouldn’t be afraid of a 5 year old 100,000 mile Prius. The car got some good exercise. And deals can probably be found. 

I say, buy the latest Prius you can afford, … perhaps no older than fourth (2015+) generation? Toyota, as much as they are building the best hybrid, … are still learning/improving as time passes. Like in,  …next Prius will, for sure, be better than the last!

As to milage on used hybrid for purchase? Well, lower the better, but 125,000 kilometres on the clock (sorry, I’m in Canada) is probably not far from the limit that I would consider, that is, if my purchasing is based on buying used hybrid for a long, long time keep. But that’s me, … no hybrid fan at this junction in time (… don’t like the driving experience!)

F.S.

I'd say no older than 2011 ideally a bit newer than that.