As far as using your 2012 version to maintain your business, go for it.  It will work fine until the program becomes corrupt on disk.  You'd need to do a reinstall in that case, which can entail some hurdles, but you should be good.  As far as sharing with your (tax) accountant, they would accept a backup copy of your file (securely on line or USB drive) and simply convert to whatever version of QBP they are using.  It's not always bullet proof. 

I recently imported a backup from a 2006 version to my 2015 and it was only functional the first time I opened it.  After this, it would become corrupted and I would have to go through the process again.  It was annoying, because I have done this in past years and not had any problems.  A bother, but I was only extracting some particular information, for which this sufficed.

Cheers,