Dual Citizenship? Do I Qualify?

I've been reading sooo much conflicting information that I just don't know what to believe.

My father was American. Has a USA birth certificate (Which i have in my possesion)
He passed away in 1990, but did not live in the USA for more than 5 years in total.

His mother, my grand mother, who passed in 2009 was born in the USA and lived there for 22 years.

I was wondering if this means I would be able to apply/ obtain Dual citizenship?

Any help would be great

A very important question is when were YOU born.

I was born in 1985... and as i kinda understand there was changes in the law for those born after 1985.. this is where i am so confused

The important date is November 13, 1986.
Since you were born before this date, your father would have had to live TEN years in US (at least 5 of which after age 14).

Those born after this date only had the requirement that parent live in US for FIVE years (at least 2 of which after age 14).

I do not believe there is any derivation from your grandmother.

I just received some further information regarding my father's standing, don't know if this could help change my potential for dual.

My father was a US Citizen (I;m told Natural Born Citizen)
He was Drafted into the US Army and was even given a draft Number. He was called to washington DC for Physicals but citing hardship his location was changed to Plattsburgh. NY
However, prior to his physical testing the draft stopped.

In anyway could this help me obtain my dual?

No. He did not fulfill the time in US requirement.