I'm not sure if what you've been told is entirely true - what is true is that the new leaves and fruiting stems emerge from the centre of the plant, pushing their way up through existing leaves, so its possibly true that you risk damaging new growth you can't see by trimming existing leaves. The advice generally with banana plants is to let withering or shrivelling leaves remain on the plant until they're completely dry and dead, which might suggest removing healthy leaves is not a good idea. There's no good reason for removing leaves prior to flowering, and its likely best not to do so.
This link describes how to grow a fruting banana indoors, but if you read it, you will see that it talks about specific varieties of banana for use as houseplants. Not all banana plants produce fruit anyway, and some are better suited to growing outdoors because of their size, or because they won't produce fruit as a houseplant.