When are you considered an solider in the army?

I am in the Army Reserves but I haven't been to basic yet. I'm also in the Army ROTC at Oklahoma State University. The other day I was walking to cl in my ACU and an elderly man thanked me for serving our country. Not knowing what to say I just said thank you but since I haven't been to basic yet (let alone over seas) I don't know if I deserve that kind of respect. I would really appreciate any advice from any current or retired service members.