If the rest of the family use iPhones, there are advantages of in joining in, having one too
However, I do generally argue these days, that the latest and greatest is the best starting point, even if it costs more - a lot more. Apple generally provide (free) OS upgrades for a few years after the device is launched. After that it will still work, but won’t have the latest OS, and may not run all latest Apps available in the App store.
There is also battery condition to consider. Battery life expectancy is largely determined by the amount of use the device has had, in terms of charging and discharging, rather than its age. So a two year old phone that’s been used incessantly, requiring a charge twice a day, might be starting to deteriorate. A four year old one that’s spent most of its life on standby might have a battery pretty much good as new. But you can’t tell the difference from looking.
I tend to buy a new payg phone outright, every few years. I reckon it works out at a reasonable cost long term, and for the first few years, I get free updates to latest and greatest iOS. My current iPhone a 5C, is five years old, still going strong, battery still good as new, but stuck on an ancient version of iOS. I’ll be seriously thinking about treating myself to a new iPhone in the very near future, just waiting to see if any new launches happen in the Autumn... then again, it’s likely to cost nearly as much as my Dad’s first brand new car, a ford escort, in 1970.