It might be an interesting blog, especially if it will continually be updated with passing other life milestones.
And the age of the book's subject wouldn't necessarily be a barrier. How popular was 'The Secret Diary of Adrian Plass' ?
But, to be honest, the subject of how someone ELSE met their partner just doesn't seem interesting for an entire book. How many times have you begged your parents to tell you the story about how they met? Dozens of times? Two times? Never? Would the story of how a couple like them met be enticing enough to make you buy a book ?
How many books have you personally bought that are similar?
It could be made to work, however ... James Harriott wrote dozens of books about wandering around in fields full of cows that were wildly popular. (Note: Generation gap -- this was a LOOONG time ago in internet years)
It might be worth checking out a format like this one
'Blog Daddy' and see how it transforms a series of incredibly mundane activities into something incredibly interesting.
It also keeps a wonderful flow - I wish my writing was as good.
Good luck,
Mac