How much does a car's reliability decrease with age and mileage?

I'm considering changing my 2009 vectra for a 2014/15 insignia. A new car is always a nice idea but one of the big factors is reliability. At 70k how likely is my vectra to let me down? It has been regularly serviced. Changing cars is obviously expensive but you get a new car out of it, I'm not a fan of pouring hundreds or even thousands into repairs on an older car. I know there are probably cars more reliable than the insignia but then that's reflected in the price, a 2014 insignia with 20k miles is a similar price to a 2012 Honda Accord with 50k miles (that bit closer to some major repair?)
So what I'm wondering is how much does reliability decrease with the age of a car? Clearly even a new car can break down but at what age does reliability fall off the edge of a cliff? I assume a 1 and 2 year old car would be similarly reliable, how about 5 and 7 year old for example?

Hardly if you know how to diy maintenance

There's no definitive generalized answer to your question. Every car is different, depending on how it's been maintained, how it's been driven, and whether it's been wrecked. The best indicator of future reliability is a car's current mechanical condition as determined by a thorough inspection by a qualified mechanic.

If you are PERFECT with the maintenance then MOST cars will last DECADES
if you are bad with the maintenance most cars will last 4 to 5 years

The older and higher mileage a car gets the greater the chances of repairs.

Does an occasional repair make it unreliable? I don't think so but when my fuelpump went out and my car didn't start at Walmart and I walked home 2 and a half miles thru rough terrain, it was a bit of a pain.

Went back the next day and the car cranked and I went and had the fuel pump replaced.

I've had a number of similar needed repairs over the years. None major but each requiring a repair. Most of the time, it didn't break down on me.

But I knew it needed something.

Your Vectra should give you at least another 50k of "major" repair free driving.

Every thing depends on good driving habits. And good servicing… When's the last time you checked your tyre pressures? Probably over 95% don't… Its little things like that… Keeping the car really clean. You keep an interest in the car when it looks good… I could afford to buy a new car today. But our bmw 528 still looks and drives like new. Its 18 years old. If I got rid of it I doubt if I could find a better drive. And my wife would not be happy! She still loves it… So no to your question if you really care for it