Yes. Similar experience here. I moved countries at 40. The first few months it feel like being 20 years younger. I wanted to see everything and went around discovering each place possible.
But, I am not young anymore. Nowadays, my new country is my new home and it feel cozy an familiar and time passes faster than ever.
> This also happened to me when spending six weeks backpacking in Europe.
For me it took longer. I have visited Japan 5 times, usually 5-6 weeks each time. I have visited temples, museums, parks, events, ... The last time I spend half of the time shopping. As, I felt that each new temple is similar to the previous one.
Even traveling to South Korea, and China it does not slows time so much. I guess that the similarities with other Asian countries makes my brain feel like "I have seen that one before".
I would be very interested in knowing if the problem is just age or to have seen already many things. Probably a combination of both.
This also happened to me when spending six weeks backpacking in Europe. At some point, the novelty itself became routine. Another castle, another hostel, another view, another language, another transit system. I knew it was time to head back to home base when I felt like I was losing the capacity to be awed by things that were objectively awesome. A couple weeks of being stationary was all it took to get that back a bit.
In order to slow down time, you need not just novelty, but also changes in real circumstances.