My experience is it is completely possible to increase your load.
A few years ago I heard about a set of techniques which apparently made sex better and increased your load, and made you shoot further. I was quite sceptical because it sounded like some old bit junkmail... But gave it a go anyway.
First thing was to drink lots of water, as everyone has been saying. Second was to keep sugar almost completely out of your diet, and protein high.
The main bit was to exercise your PC muscle by contracting it. I was told to do this once a day as many times as I could manage.
When I started doing this I did notice an improvement, although at first it could have been the excitement of the possibility of that! But after a month or so there was such a huge improvement I wondered why noone else had ever told me about it.
Now 4 years later I can shoot about 20 times on a good day, which is basically a 2-3 times improvement, and it feels fantastic.
If anyone wants more info just say.
Hope this helps someone!
Danny