It's hard to know. 11 or 13? 128GB or 256? 4 or 8GB? If more the former, then perhaps not so good. If more the latter, then pretty good. My daughter has a 2011 13 with 4GB. Runs El Cap just fine for her purposes.
I have a 2013 MBA 13'', 8GB RAM 128GB HDD. Lovely machine, very happy with it. Runs El Cap like lighting, graphics not too hot, but to be honest, pretty much the same as a 2016 MBA.
I was determined to get 8GB RAM because of constant RAM problems on my previous whitebook 4GB, but I may have underestimated how much difference the high speed SSD in the MBA makes. I might have been fine with 4GB in the MBA, I dunno, but Activity Monitor seems to never ever show any RAM issues in the MBA. At the time i got the MBA, required RAM was on an upward spiral, but the last few years amazing steps have been made in using less RAM. The 8GB may come in handy for future revisions of OSX though.
I do wish I'd gone for the 256GB - only 128GB has been a severe issue for me. I have a PNY 128GB SD card, but it is nowhere as nice as having 256GB onboard.
So, basically, if you are offered an 8GB RAM, 2566GB SSD MBA, grab it. It's a wonderful machine for photoshop, editing etc. If it's 4GB / 128GB, then be wary, its days are numbered, but will still be fine if you only do text documents / internet based stuff.