When you say old iPad, what model is it that you actually have? The first generation (2010) just don't have enough RAM, or fast enough CPU, to cope with the complexity of modern web sites. I doubt the second gen, "iPad 2" from 2011, is fairing much better either.
As you say, turning off JavaScript may help prevent crashing, but at the expense of the web site not actually functioning as intended.
It's just the inevitable march of IT progress, unfortunately.