Pre-flowers don't turn hermi. You'll do yourself a big favor reading up on what marijuana plants are about -- their life cycles, their needs, their quirks, and the things that can influence not just a good harvest but getting to harvest at all.
You can pick any one of a number of reasons to force flowering. For most people it's space. Look at your plant. If it doubles or triples in size, will it be bigger than your space? (not important if you're growing outside) At 14 inches at 2 months and 7/8 nodes, I'm guessing you have a sativa dominant strain (or the plant just hasn't had access to a lot of light) and if so count on tripling in flower.
Your plant is naturally ready to flower if you have alternating nodes and pre-flowers. Even then, flowering won't take place until the plant is on a 12/12 light cycle.
Good luck!