^^Not very long, you'll develop a bit of a pattern, but hopefully still plenty of enjoyable moments. My boyfriend and I have been together for just over a year, and he was my first. So needless to say, he kinda let the cat outta the bag. I'd always kind of assumed I'd be into sex once I actually had it, it intrigued me in my awkward stages of puberty and I used to get jealous listening to my friends who had boyfriends talk about it. So we used to go at it pretty often, whenever we saw each other, and more than once each time. I don't see him as often, so i'm gonna say 1x-2x per week on average. But there are periods where we miss each other a lot and we just go crazy, these instances are a rare treat.
I disagree with people who joke that the longer a relationship goes on, the less exciting and frequent sex becomes. If you're in a happy and healthy relationship, you and your SO will find a pattern that works for the both of you, which might be once a day or once a month. It's all about finding a balance that you're both happy with, and that could take some time for some couples. I wish you all long and happy sex lives lol *toast*