Hi,
I guess one is ready for sex if both have a lot in common, have almost the same moral convictions, share the same sports, hobbies, mostly the same educational backgound, financial status, intellectual capability and sexually compatible. If both are compatible , have mutual feelings,have common goals for the future, have the chemistry, then that's the time to have sex to make the two closer. This process takes longer than the one night stand wherein the 2 people just feel like having sex , even if they are not compatible. This kind of relationship is mostly short-lived and does not go anywhere.