How would I read and respond to a PM that doesn't have a topic line?

sorry i didnt want to right a topic for it

but really how old are you?

If I try to send a PM without a subject, it says "You must enter a title", so I'm not sure how this PM was sent.

Ask the sender to resend with a subject??...

Looks like the subject of the PM has been posted above so all is well.