I don't think Grognard is so much a title that you earn, more of a loose concept that you can find yourself fitting into if you identify with a certain set of grognard values.
Personally, I think the road to self-discovery in this context is to go over to Dragonsfoot, read it for three hours, and if you like what you're reading, it's pretty safe to assume that you're in the right camp.
If you can answer yes to any of the following - you might be a Grognard
1. You played 1e back in the day. Regardless of whether or not you have played any edition since, you are certain that 1e was the best.
2. You are certain that when TSR changed the artwork on the 1e manuals, the game suffered.
3. You believe that Wizards of the Coast are an evil mega corporation, just like Sternmetal Horizons or Ling-Standard Products.
4. Any new edition of any RPG (except Runequest) is automatically a money-grabbing sell-out and just about dumbing down for the kids' market. If and when a D&D 5e comes out, you will yearn for the good ol' days of 4e.
5. You call game designers of yesteryear by their first names. "Greg", "Gary", "Dave", "Sandy".
6. You have had several late night debates over exactly which issue of White Dwarf represented their turn to the dark side.
7. You constantly berate RPG companies for publishing games with splatbooks and other player accessories for their mercenary attitude, and you can't understand why they have to do it - despite the fact that you have a boxfile full of photocopied character sheets, and to the best of your knowledge they were photocopied from a single set of the orange ones bought in 1984 by your brother's friend's DM.
8. You have written a review for Village of Hommlet...
9. ...in the last 12 months.
10. You believe that "real" dice should come with a crayon, and that the "real" way to roll d% is to roll two d10s simultaneously and name the 10s die as late as possible.
It all makes sense then.
