UK Car Repair: High mileage diesel engines, high mileage, petrol cars

Question
I am in mid debate regarding high mileage modern diesel engines, namely peugeot 306, yr 97-99 apx.
my question: Would the engine be just running in or still youthful, say at 100k in comparison to a petrol car of similar age/mileage?
My own thoughts are that leave petrol cars of similar stature well alone, but diesels are far more robust and have a long way to go before they reach the same "leave well alone" status.
It is really so i can have a second opinion as i have heard this many times in the past, but now it has become aparent & would like to confirm what i feel i already know, also if i am wrong i want to know as not to make the mistake of that being a crucial decision maker. I expect any car of that age to have its faults but a better engine is certainly one less thing to worry about. All the above is in general terms.

Answer
There is no way I can say that a particular diesel engine is OK at 100 K but generally diesel engines have been 200 K + engines. But then there are some gas engines that are thought of as 200 K+ engines like the 6 cyl. Jag and some MBZ engines. I do think you can say that most diesel engines are merely at half live or less at 100K.

That is my opinion.
HMF