danc - this is a hard question to give a simple answer. There are so many factors to consider - the type of kit, quality of kit, how much oak is involved, white wine or red wine, how many carboys you have. There are also differing opinions on bulk aging vs bottle aging.
Generally, I will not bulk age white wines ( they may stay in the carboy for a month or 2 until I get around to bottling them) - some of them are meant to be drunk young. I will bulk age red wines in the carboy for 3-6 months. Others on here bulk age for a year or more.
I would suggest you use the search function for bulk aging wine and read some of the threads and that will give you a good idea of some of the discussions.