Any criteria involving age, physical characteristics other than not being obese, or virginity are unrealistic. Of course, if you're ugly you'll probably end up dating another ugly person, but at least then you know you like each other for your personalities.
For personality traits, generally being nice to them (and in general), fidelity, not gossiping/excessive shopping, and being a good cook can never hurt.
For long term-relationships, it's also important to be a good conversation partner and be able to diffuse arguments without huge shouting matches.
If you change yourself with only the goal to date someone, one of you is going to end up unhappy in the long run, either him for feeling misled or you for feeling trapped.