I think the answer depends on how long a couple has been together. If you’ve been together a few months/less than a year, I think it’s reasonable to wait another year or so for a proposal.
But in your situation I voted one month. After 4.5 years together, he should not need more than 30 days to figure out whether he is ready to speak the words: “Let’s start making plans to get married within the next year or so.”
I don’t think it’s a good idea for you to keep your fingers crossed, wait patiently for him to make a move, and “chill,” as you said. You may have to let go of your dream of having a romantic, surprise proposal. If you stay quiet and passive about this, you’re sending him the silent message that you are OK with status quo, you’re in no rush either, and you’re OK with dangling out there with question marks about your future(s).
After 4.5 years, you are within your rights to speak up — nicely and calmly and lovingly — and let him know that this is important to you, this is your life too and you’d like to know what his intentions are.
Try to find a time when you are both relaxed and in a good mood. You don’t have to tell him what to do. But you are allowed to tell him what you want and need.
He is free to agree or disagree with you. This doesn’t have to be an argument or an ultimatum.
My DH was dropping marriage hints after a year or so of dating, but after 14 or 15 months of dating and no proposal or specific discussion, I was getting really antsy and I spoke up one night when we both were in a good mood and relaxed. I asked him where he thought all of this was going. We both shared that we loved each other so much/wanted to be with each other for many years to come, but still he didn’t say anything specific. So I very gently and nicely nudged him and said as lovingly as I could, that I couldn’t stay in a relationship indefinitely without knowing whether we were going to take our commitment to the next level within a reasonable amount of time. There was no argument, no ultimatum, no “you’d better propose to me or else” as you said…. I just let him know what my bottom line was. Much to my relief, he suggested we start making plans. He did a formal proposal a few months after that, and we ended up getting married on our two-year anniversary.
If I hadn’t given him that nudge, we might still be dating!
It sounds like your SO loves you a great deal and is very serious about you… but if you don’t say anything, this could drag on for another 4.5 years.