I don't find it particularly sad, as I choose to read the ending as the end of long and happy lives together. I would have preferred something a little more subtle, like them sitting together on a park bench or something.
It does feel like the author is making a statement against commenters demanding a timeskip epilogue for every romcom, tho
30.000 days is around 82, middle scholers in japan are around 12yrs. they're nearly 100 years old in that last pic, that's as good as it gets for most people.