That's brave of Miku to ask someone what they want for their birthday without saying that it's for their birthday.
Also, r/5ToubonNoHanayome is theorizing that the guy is Maeda, from chapter 25, who is shown to be married with his wife pregnant.
@00nowhereman I theorize that the marriage is still five years in the future from the present.
1. In chapter 25, the chapter is titled "Day 2000" which is approximately five years.
2. In chapter 68, the quints mentioned "five years ago" along with the picture of themselves, looking more aged and mature, with their wrinkly grandfather which supposedly is taken in the future.
Conclusion: marriage is still five years away. The series is still far from over.