Final answer:
The sentence is capitalized correctly; 'Post-Reagan' is a proper noun referring to the time following Ronald Reagan's presidency and therefore should be capitalized, while 'era' is a common noun and is not capitalized.
Step-by-step explanation:
The sentence “We have been living in the Post-Reagan era” is capitalized correctly. The term “Post-Reagan” is a proper noun because it refers to the historical period following the presidency of Ronald Reagan. This period is often characterized by political, economic, and social policies and ideologies that were influenced by Reagan's terms as president. As such, it merits capitalization. Additionally, 'era' is a common noun and is not capitalized unless it is at the beginning of a sentence or part of a title.