How many years can an iPhone last?

Six years ago, I replaced the battery of my old iPhone 8 and gave it to my mom, while I upgraded to an iPhone 13 Pro.
Today, after six years, I replaced my mom’s iPhone 8 with an iPhone 13 Pro, and I upgraded to an iPhone 17 Pro Max.
Counting it up, the iPhone 8 has been in service for 9 years.
When I gave my mom a new phone, she said the iPhone 8 still works very well, doesn’t lag, so why replace it, it’s just a waste.
Of course, I also gave her the 13 Pro, and she was very happy—an all-around upgrade.
But it’s not over yet. My aunt has been using an Android phone, and that thing is so laggy, full of rogue apps and notification spam.
Then, the iPhone 8 ended up in my aunt’s hands again, and she said, “Hey, it’s not lagging anymore.”
I feel that the iPhone 8 can still serve for 3 more years, and the iPhone 13 Pro can last about 5 years, of course, with a battery replacement.
Right now, for me, spending a few thousand yuan on a phone that lasts several years is reasonable.
I bought the iPhone 13 Pro for 8,799 yuan, and using it for 10 years isn’t unreasonable.
The iPhone 17 Pro Max cost 11,999 yuan, and I expect to use it for about 10 years.
In my hands, it’s been about 3-5 years.
I personally take good care of my phone, always use a case and screen protector.
I can’t get used to a naked phone—not to keep it looking new for resale, but just so I can give it to family members later and it can still be used for a few more years.
Elderly folks just use it for listening to music, making calls, watching videos, chatting—enough!