My car hasn't done vast amounts of miles (short of 60000), but already at 30-40000 I would say I noticed it's ability to accelerate has dropped. It is still OK for my use and the fuel efficiency is good (60+ US mpg, 70+ UK mpg). I am guessing reasons would overlap with some of these causes, but wanted to ask somebody more knowledgeable than me.

It is a standard turbodiesel (no common rail or variable vanes) with particle filter (DPF) and catalytic converter, manual transmission (and having read other posts here I think the clutch is fine). It is a 1422cc 3 cylinder engine with a balancing shaft, although I don't think that matters for the arguments.

Things I can think of are DPF (although it does not appear to give any new/unusal problems), air filters, worn bearings giving more resistance, perhaps the turbo is worn/less efficient (why?), but apart from that I am not sure what causes this.

I don't think losing the "new car effect" is uncommon or a problem as such, I am curious about the causes. Thank you!