I was terminated after passing the 12 weeks LOA period according to my companies policy

I'm not licensed in Massachusetts, but generally speaking employers have a lot of freedom to terminate employees. Unless you have an employment contract that states otherwise, you are considered an at-will employee. Your company can fire you at any time and for any reason (or no reason at all), even if you are injured or ill. There are exceptions. If you have reason to believe you were fired based on an illegal reason (race, religion, sex, etc.), you should talk to an attorney.

Unless you had a contract to the contrary, the Family and Medical Leave Act only provides the right to job restoration if the leave is 12 weeks or less. An employer has no obligation to hold a job open to someone who otherwise cannot perform the essential functions of the job.

I would be interested in speaking with you about the age discrimination question; you may have a claim if you could show that younger workers who took more than 12 weeks of leave were restored to their positions.