Hi. The Church really doesn’t get involved with when a person should get married. It is really a matter of the heart and knowing if you can fulfill your spousal duties according to what God intends for men and women. If you feel ready to commit to her for the rest of your life, and if you are ready to embrace sex as unitive and procreative then you pretty much have it down. Of course, it is prudent to make sure you can provide for the well-being of a spouse (being financially independent, having goals in mind). If your girlfriend is saying she does not want to settle down yet, that is something that she needs to decide on her end and neither you or the Church can be responsible for her heart. BTW, have you looked into NFP? Being open to life doesn’t mean purposefully having kids right away, it just means not contraception and rejecting God’s hand in your marriage. I have been married nearly 3 years and do not yet have children.
There is no duty to get married by a certain age or dating time limit…but you must treat each other with dignity and that means one should not waste the others time if there is not intention of marriage at some point. Just ask her to be honest about her plans for the future and if they involve marriage and then allow yourself to make a decision based on that. Remember, a man must be willing to die for his wife as Christ died for his Church. I think when a man fully comprehends that and feels he could follow that, he is ready for marriage. So then you have to ask yourself, if I am willing to die for her, am I willing to simply wait x amount of years for her. Also, if she isn’t willing to give you a reasonable way to persue marrige with her then you have to ask why.