How do you set the time on a peugeot partner van 1.4 , and what is the average mileage for a 1.4 petrol

Do u have experience with using a strobe light, & watching the timing marks on the flywheel? Then u rotate the distributor a slight amount. l think ur 1.4 engine is one of the TU versions? or is it an XU with fuel injection??
l am pretty sure u have a TU3 carburated 1.4 litre engine. The timing should be 4 degrees BTDC at idle speed of 700 or 750 rpm.
Basically, here is the procedure.

1. warm up engine to operating temp.
2. stop engine, remove plastic cover over the flywheel & timing marks.
3. slightly!! loosen two distributor mounting bolts
4. restart engine, fasten strobe light to #1 spark plug & battery. Measure idle speed with hand-held tachometer if possible.
5. KNOW in advance if ur timing marks should be zero or as much as 10 degrees BTDC (Before Top Dead Center) at a specific idle speed rpm's. The engine is spinning counter-clockwise as seen from the gearbox side. TWO slots in the metal plate are: upper = x degrees BTDC. lower = TDC
6. slightly rotate distributor until the warm engine is timed according to specs.
7. retighten distributor bolts, replace plastic flywheel inspection cover.

Get help if this is ur first attempt. A spinning engine is dangerous to fingers, clothing, long hair. Do not be careless.

Average mileage varies between countries but in the UK average is considered to be 10-12k miles a year, so for example a 4 year old car should have covered between 40 and 48 thousand miles.

On a side not though as long as the engine has been correctly service at the appropriate intervals you should not really have any concerns on an engine that has done less than 100 thousand miles, even if this would seem high using the above calculation.