In my experience, I would say maintaining quantity of cum and velocity is definitely linked with maintaining a healthy diet, good hydration and maintaining your frequency of sexual action, along with doing strengthening exercises.
I compare with my friends of the same age and hear the same queries in respect of the waning of their sexual abilities, and in particular the quantity and velocity of cum and even their actual orgasm.
Having had an interesting chat way back about 12 years ago with doctor acquaintance and mental noted her indicators on making sure you maintain and strengthen.
I have maintained the traits as mentioned above and also added in flexing and strengthening exercises down below. And have not seen any lessening of quantity or velocity of cum.
And if anything my precum amounts are greater and kick in far earlier in the process.
The simple thing of when your relaxing or just going about your daily routine and have moments to concentrate on it, and I've seen me doing it at a meeting while sitting.
Flexing down there. And sometimes clenching your buttocks and flexing your thighs to increase the flexing in your groin area.
It may just be a coincidence, that I have been able to maintain everything as it's always been, but I think otherwise when I compare to friends.
I have always cum at least twice a day throughout my life and still maintain a high sex drive. Which may well be uncommon and some friends say not natural, but as someone said in the previous comments, if you don't use it you lose it.
And I believe you've got to maintain things to make them last.
Dougie.