I need to take a different perspective here…
Forget about the proposal for now, and setting a date. When going through Catholic marriage prep, you aren’t supposed to set a date until you’ve taken the foccus test.
There are 2 elements to marriage prep: Discernment, then actual preperation. I STRONGLY encourage all couples to go to “pre-engagement” counseling with a priest and a mentor couple. Don’t get caught up in wedding fluff. Make sure that this relationship is sturdy, focused on Christ, that your morals and values are in line, and that you have spent a ton of time praying together. Get a spiritual director. Do all this before you buy a dress and put down a deposit on the reception hall. When money is tied up in a wedding date, the less freedom you have to say “no”.
I am in no way supposing anything here, but his avoiding setting a date are sometimes a symptom of when a couple is sexually active before marriage. I’m not asking if you are, but one leads to the other often.