It's entirely normal in the industry for people to go from zero-CFI in six months. The FBO folks sometimes take longer due to work or whatever.

An Academy Grad CFI who goes to work for his school has an advantage in that he knows all the profiles, procedures, airspace, and aircraft. Also, the school will start new CFI's on something easy, like privates or commercials, and have the more experienced CFI's do CFII and finally MEI work.

There are a few tasks which actually require a sign off from a CFI with 2 years experience and/or 1000 dual given (I think). This is why those schools would also hire "Street CFIs".

Many FBO CFI's do it for a hobby or are professional CFI's, whereas the academy/big flight school types are obviously going to split for an airline before the reach high levels of dual given.

An advantage to working at an FBO is that sometimes you can command $30-40/hour depending on the type of instruction. Typical flight schools pay $8-10 for CFI, and maybe $15 for MEI or check airman.