Just my thoughts. I think buying ANY 8 year old car is a gamble. Some will be better than others even across the same model and marque.
A clutch and gearbox will wear out quicker the more it is used. Hard to tell to tell and you cant always go on mileage. Outward condition can give a clue and service/MOT history. Always go into such a purchase with a fund to repair, if you cant drop £1000 off your purchase budget.
I bought my 3 year old C'eed in Feb 2019 at 23k miles now with 52k miles on the clock, it has cost me 2 x services (dealer) and 2 x MOT's and a full brake pad replacement (not dealers). Only other items are a headlight bulb, wipers and a washer jet - mostly maintenance items.
My dad had an Hyundai i40 2013 (63) and the clutch was going on that (no other issues) at just 46k miles before we sold it - there were some common reports on that model.
I think you would have to replace the clutch a bit earlier on the Kia/Hyundai models and I would say between 80-100k and while i haven't had any issues yet I think it is down to the fact they aren't quite as hard wearing as other marques. Others will differ to say.
I expect to replace my clutch around 100k of which I will have no issue with that - you might be lucky as the 1.6U2 engine I read does not have a DMF saving further money.