As Del said, if we take all the data from the finds on the Mary Rose, the average bow length is 77", and the average arrow length is 30.5".
There are a couple of guys who shoot in the English Warbow Society who shoot beyond that length - and do so exceptionally well. One is currently shooting 140lb at 34", but as Mark wrote in his blog post the actual benefits are quite small, if there are any at all.
One of the problems is that it's very hard to find that perfect length without shooting a full weight bow. There's a wonderful point at the end of a medieval draw where everything locks together and you physically feel all the weight of the bow sit on the shoulders and back and your arms stop feeling any strain and you could essentially hold it there forever.
The window to that point is tiny - an inch or two either way and it can still be quite awkward feeling.
Again as Del said, try it with a very light bow or length of elastic and you can draw back to some ridiculous length, but get the weight estimated properly by stacking the elastic and all of a sudden you'll be able to draw until that wonderful moment when it all gets very easy, measure it at that point and there's your ideal draw length.
It's not usually over 32" or so, but if it's 33" or even 34" at least he will be in good company, amongst other gorillas who shoot warbows