Six month anniversary promise ring gift?

So I wrote another post on glow a while back about whether I should propose to my boyfriend or not at some point. However life had put all those thoughts on hold but now we have been together almost six months and we are serious about each other and I feel like I want to celebrate because this is both our first serious relationship and I feel proud of us. So I thought maybe now would be a good time to buy a promise ring? Or rather a set of matching for us both. Do you think this is a good idea? Then I'd let him propose at a later date when he wants.. We have joked a bit about marriage though not really discussed it properly. But I think we are both open to it in the future when we have been together longer and our circumstances are improved (finances, health, ect). I am 24 in August and he just turned 30. Do you think a promise ring for a six month anniversary would be a sweet gesture? Thanks :)