At the moment, yeah - over the years it's been generally trending upwards, with every other generation gaining a year up to the 5. It's been a little less predictable lately, but still trending up - 5s and 7 got six years, 6 got five years, and 6s got seven years. Remains to be seen whether they'll keep going up in future - I wouldn't be shocked to see the A11 devices dropped this year, which would put them at six years, given how many features they've been left out of over the past few releases.

But also worth noting is the 5s and up are still getting security updates, which is pretty exceptional. That's over nine years of at least some support at this point.