16 at the beginning of the story, it's been long enough for her dresses to become too short so I would say that it has been quite some time since then.
I would assume her to be at least 18 at this point. So what we have is basically a big age gap relationship, which personally I find to be shady IRL cuz we don't know if stuff like grooming has gone on.
I looked for other context clues but there are none. Just a significant height increase since she moved in. At 16 growth is super slow (I grew like 2cm since I was 16, I'm almost 20 now. )

I don't wanna say it cause the story was good but
.. is this pedophilia like... she is 16 he is 60+ it feels wrong on so many level but I still like the story if I ignore everything....