So recently I have been doing some genealogy stuff for both of my parents through ancestry.com and a couple of other sites; I have come to find out that my Mother's grandfather was from Mexico. Do I qualify as Mexican-American? Should I mark this on my apps?
I've been marking "Hispanic" things sporadically throughout life and Latin culture has always been a big part of my life and upbringing. We just never knew exactly from where these traditions were from. There was early speculation in my family that he was from Ecuador.
What have you been putting on your college applications? Job applications, Census surveys, etc.? And how do you define "Latin culture", exactly? Because there is no uniform "Latin culture". If you've been identifying yourself as white all this time, you need to continue to identifying yourself as white. Otherwise, you'll run into problems.
EDIT: I find it interesting that you said that you just found out about your "Mexican heritage" by looking at Ancestry.com, and then turned around and said you've occasionally seen yourself as "Hispanic" through the years. What's the story there?
In community college I listed Hispanic and on the application to the university I ultimately graduated from I marked white, because there was no option for "Hispanic"; it had many nationalities broken down into individual groups. On job applications I have gone between white, Hispanic and decline to state. I am a non-trad applicant, originally from SoCal, and growing up and into early adulthood, I always felt listing it would actually harm me and not help me.
I define Latin culture in this context as loosely being: cuisine, art, and values.
Like I said above, I have always known that my Mother's Father was Hispanic, however we never knew from where. We didn't know if he was from Mexico, Panama, Ecuador etc.. My grandfather had 2 wives, his first wife was also Mexican and they had one child and then his second wife was American and they had my Mother. Growing up, my Uncle who is full blooded Mexican was very much a part of my household and family, imparting the culture into my life deeply. My Mother also brought the culture into our household as well.