I didn't see anything that mentioned discounts for seniors or maybe didn't pay attention. I would recommend that you call in to check. Also it's quite huge. It'd be recommended that you plan in advance for the sections or areas of interests, and take breaks in between, to rest and enjoy.
23 dollars. https://www.mfa.org/visit
Call and ask. Rates may vary on weekends and for exhibits.
Try your local library they often have Museum passes that you can check out which will either give you a reduced admission or a free admission for two people that's what I use
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