What is a synonym for "girlfriend"?

I'm in my mid 40s and dating this lady of a similar vintage. I am trying to find a good word to describe our relationship, but "girlfriend" and "boyfriend" seems inappropriate for us. It reminds me of those forty year old guys who say "I'm gittin' down wi ma hommies." It communicates, but it seems out of place.

Perhaps it is the "girl" and "boy" part that bothers me.

Any suggestions for something more appropriate?

Depending on how comfortable you are with the mixed connotations of the following suggestions:

• lover
• partner
• companion
• mistress
• significant other

You also just refer to her by name which would probably be more polite. Depending on the context you can use the term "dating":

We are dating.

Sue and I are dating.

We went on a date.

Sue is my date.

Edit: Not that there is anything wrong with girlfriend. I understand the desire to avoid it but it has its use even amongst older couples.

How about:

Sweetheart

A common term to refer to "your lady" i.e. That one, over there, she is my sweetheart.

Kinds of indicate a closeness to your heart :)

Also, if you like something more passionate:

flame

I wouldn't use "mistress", as it has a nuance that doesn't quite describe your relationship, or "partner", as that makes it sound too businesslike.

I personally find the term beau quite endearing and appropriate for men of all ages. The feminine equivalent is belle, which is also nice.

Or you might like sweetie, if that's not too sappy.