Hm, odd that, the newest laptop I have here is from 2016 and with that just past your threshold. It works just fine, performance is no problem, the battery holds for around 5-6 hours. Maybe it helps to say I a) don't buy Apple products and b) only use Linux? Nearly all my laptops are Thinkpads, all of them run Debian in some form or other. From the ancient (T23) through the old (T42p) to the relatively modern (P50), all of them work for their intended purposes. They are built to last, if something breaks it is easy to fix but things rarely break. The batteries are easily replaceable, the same goes for the keyboards.
In other words it is more than possible to use laptops beyond those 8 years as long as you buy the right ones. Performance is fine as long as you run the right software, i.e. not software made by a hardware vendor who depends on a regular replacement cycle.
Well, I haven't always bought Apple Products. My first laptop was a Toshiba and it lasted five years. Then I bought a used Thinkpad, I can't remember the model now but it only lasted about three years. My next computer was a thinkpad, I think a T203 or something like that, and it died after five years also (just stopped booting).
I also installed Linux on them too and the battery life was not great either. I could be an outlier but I've not had good experience with Thinkpads even though I liked them. My older Macbook actually lasted the longest.
I never bought any Apple products but did get two items gifted over the years due to seemingly standard defects which render them inoperable: a 'late 2009' 27" iMac with an inoperable video card (a standard defect in these things) which I made operable again by toasting it for 5 minutes and a 2011 Macbook Air with a broken keyboard (qwertyuio keys dead, again a standard defect in these things). To fix the latter I'll have to get an new keyboard, rip out the old one - which Apple in all its financial wisdom riveted down with some 30-odd tiny rivets so as to make it more difficult to economically replace the thing - and screw in a new one. I'm not yet clear on whether I'll go so far to revive the thing but the level of planned obsolescence in Apple products is quite disgusting to me, seasoned user of previously owned hardware.
In other words it is more than possible to use laptops beyond those 8 years as long as you buy the right ones. Performance is fine as long as you run the right software, i.e. not software made by a hardware vendor who depends on a regular replacement cycle.