I am fail to understand that why your boss will be hurt, if your claim your Gratuity...?? Are you thinking that your boss will be hurt just because he will need to pay you...!!
Gratuity is like an award, which is given to the employees for their dedication towards organization and work for a long time period. As mentioned, you worked 12 years for that organization, which is a very long period. In my opinion, your boss should be happy while paying you gratuity as you have given your 12 precious years in growth of that organization. So, just go ahead and claim your gratuity.
If you will wait for 10 years, then it is possible that the scenario will be changed after 10 years. And might be possible that you will have to face so many problems at that time as mentioned by the other learned members.
So, in my opinion, just go ahead and claim your gratuity without delaying.
Hope this will lead you to take a good decision.
31st December 2013 From India, Delhi