You may find that an adult doesn't stimulate the breasts in the same way as an infant does, and this may also reduce the amount of milk. Apparently when children reach a certain age (around 6-8years from memory) they lose the ability to suck using their tongue in the same way as an infant and it makes it harder for them to get the milk. The sucking action of a baby helps stimulate the breast to make more milk, so I'm not sure if your breasts will produce as much milk as if an infant was suckling.