I just bought a renewed macbook air 2016 with yosemite installed. Am I suppose to update this to the latest Big Sur?

Ignoramushere wrote:

How many years should this computer be good for?

It will be good for as long as it continues to do whatever it is you bought it to do.

My first Mac is still working. I bought it in 1985. I upgraded to an SE/30 when I needed to do things I didn't need to do back in 1985. I replaced the SE/30 shortly after the first iMac came out, as I recall that was 1997. As far as I know it's still working too.

And so forth. If you want to know how long Apple will continue to support your Mac, that period of time is very approximately seven years. You can research Apple's list of "vintage and obsolete" products here.

I have an iphone 6s+. So, I suppose that will be dying next month.

??? I don't know what that means.

... It was only $420 on amazon.

I overlooked that part. Amazon Marketplace, presumably?

Return that Mac to Amazon for a full cash refund.

There are too many inconsistencies in your description. Not only was there no 2016 model year MacBook Air, Yosemite was superseded in 2015 by macOS "El Capitan". Yosemite was introduced in 2014, a full two years prior to the alleged age of that Mac.

If that Mac was properly prepared for resale, and that preparation resulted in Yosemite being installed, then it is either a 2014 or 2015 model year Mac. That brings it very close to Apple's "vintage" status, meaning you're not going to derive much useful life from it.

If that Mac was not properly prepared for sale, you're going to encounter a lot of problems until it is. That's a seller responsibility. A purchaser should not be burdened with that task.

Something isn't right. Return it. If you want to save a few bucks on a new Mac, purchase one from Apple's Refurbished and Clearance page.

Yes: How to upgrade to macOS Big Sur - Apple Support

You are definitely not supposed to update it...if you wish to, you can update to Big Sur as the MacBook is qualified to run it. However, if Yosemite serves your needs you can leave it there.

One thing to be aware of before updating: if you update the MacBook to Catalina or later, all 32-bit apps on your Mac will cease to function so if you have any 32-bit apps that you rely on, either find a replacement app or don't update to Catalina or greater.

Regarding the Mac, I think you should start by describing what it is you intend to do with it. A six or seven year old Mac is certainly useful, but even simple things like wanting to install Pages or Numbers could be a show-stopper when Apple no longer provides versions compatible with older operating systems.

That's just an example, and it's not a particularly good one. Off the top of my head I don't know which macOS version is required for Apple's current Pages and Numbers apps, and it's still unclear which model MacBook Air that was. The point is that if you purchase a Mac to do specific things, make sure it's capable of doing them before you purchase it.

Your iPhone 6s for example may not be upgradable beyond its current iOS version, but that doesn't mean it's going to spontaneously stop working. It will continue to do what it always has, but the day may come when you want to install an app that requires a more recent operating system. Then you have to decide whether it's worth replacing your iPhone with a newer one simply because you want to use an app that didn't exist when you bought it.

Macs are no different, but if you want to derive a decent amount of useful life from one (knowing "decent" is something only you can define) I'd be reluctant to buy one that's older than those offered on Apple's Refurbished and Clearance pages. All of them are fully supported and indistinguishable from new. They might be older models, but some are current production ones.

The used market is certainly another alternative. You can certainly find good deals from knowledgeable, reputable sellers if you are prepared to look long enough, but it may interest you to know that sellers fitting both those criteria (knowledgeable and reputable) are rare. They're practically nonexistent on eBay for example. If you should come across one, their prices are likely to very similar to Apple's anyway. No joke — I'm often amused by people who pay more for a used Mac on eBay than what they would have paid Apple for a fully supported refurbished model.

Once in a while you'll find a private seller who wants to unload a Mac at a really attractive price. Usually that seller is totally unconcerned about money and just wants to be rid of it, but in those cases even Apple offers a trade-in value when purchasing a replacement. It's absolutely imperative to be a Mac expert when identifying such a find though.