was he a citizen or not? (ireland)

This is my first post. Thank you to all who reply. Having visited the official site for irish immigration, i noticed several conditions that must be met in order to obtain irish citizenship. my situation is slightly different. perhaps someone could shed some light on this:

my great-grandparents were born in ireland. their son (my grandfather) was born in the u.s. however, he moved to ireland at the age of four. he lived there for a few years and attended school. however, he did not complete any offical paperwork regarding citizenship. and, while there, he traveled to the u.k. at one point under his father's american passport. at about the age of 7 (or so) he returned to the u.s. would he be considered an irish citizen? based upon his citizenship status, could i apply for citizenship through the familial conections option?

Here is some information from the Washington Irish Embassy:

http://www.irelandemb.org/fbr.html