How long is a LOR valid? I was planning to apply for fall 2014. As the application required a Hard Copy Letter of Recommendation, I had obtained a Letter of Recommendation from my College Professor on the college letterhead.  But due to some reasons, I was not able to apply.

Now, can I use this same Hard Copy for Applying to Fall 2018, or do I need to get a recent LOR? Is there any validity period for these LOR's.
While the previous letter is still technically valid, I would strongly urge you to consider getting an updated letter or even a replacement letter from someone else. If you have done anything noteworthy since the previous letter was written, then that could be incorporated in a revision. Alternatively, you may find that someone else is able to provide a more useful evaluation of your talents and abilities.