Should the things you post on Facebook and twitter ultimately be viewed as representative of who you are in real life? Does that change with age and your situation in life?

I got into an argument with a girl I've been talking to about the relevance of who you present yourself as online relative to real life. I took the "relevant" stance, she took the it's "irrelevant" stance.

We're the same age but are in dramatically different places in life. I was an officer in the Navy and am currently leading a career in project management. She just graduated college and is in the job hunting/missing college phase.

I kind of expect the answers to vary wildly based on age and certain life exposure. Who knows? Maybe I've just got bad ideas about how the internet can guide social interaction and foster preconceptions.

(please note: this is not a question of how things should be... this is a question of how we interpret they are currently.

TL;DR: It's like 8 sentences... Not sure I can make a synopsis shorter.