johnnyrebel00 - I don't have any specific resources to offer. I do know that some series of notes may run for more than 10 years. The "A" below the date means a revision was made to the original 1963 series note. I've seen some notes that have B, C, D, etc, below the date if several revisions have been made to the original series note. Major changes in note design will start a new date series. In the case of your note, the revision was probably when Henry A. Fowler was appointed Secretary of the Treasury in 1965 by then President Johnson. Therefore, after his appointment in 1965, his signature appears on federal reserve notes, which would mean a revision of the original 1963 series note. Mr. Fowler only served as Secretary of the Treasury for a few years; your note would have been printed while he held that position.
As far as describing your note as "old" : old is a relative term; a mid-60's baseball card is "old", a mid-60's automobile is "old", why cant a mid-60's 10 dollar bill be "old" ?