I believe you said your Boston was 12 years old. Maybe you meant to say 12 months old? The best time to breed is when your dog is between 2 and 10 years old. Since you have a male, 12 years might be ok. Here is a great website to do some reading way before you decide to breed... http://www.freedogwhisperer.com/freedogwhisperer20.php
Another website is this one: http://www.dogbreedinfo.com/whelpingmain.htm