I've had one of the older (flat style) Airport Extremes running for the last 6-7 years.
Never a hiccup, just keeps going and going and going...
BUT --
If I were to replace it today, I'd spring for one of the new "mesh-style" systems that have come onto the market within the last year. Indeed, I plan to do so within the next few months.
Having said that, if you need to replace your wifi router, and have access to one of the old AE's "for cheap" (I wouldn't spend more than $50 for one, if that much), it could serve you well enough.
(Aside: you might be able to pick up the last-generation "tower" AE's on ebay for around $80-90)
But again, do some investigating on the new mesh setups (eero, google wifi, ubiquiti, netgear orbi, linksys velop). They're on the expensive side, but they do "deliver" ....