I have been fond of stationery shops since (my) childhood. I have been fond of stationery shops since (my) childhood.

or "...since I was a child."

I have been fond of stationery shops (since my childhood). I have been fond of stationery shops (since my childhood).

(): Right now, this sounds more formal. To sound more conversational instead you could write, "since I was young". If you want it to be more exaggerated "since I could walk!" To continue sounding more conversational you could shorten "I have" into I've.

I can spend hours browsing the shelves ofilled with notebooks and pens without buying anything. I can spend hours browsing the shelves filled with notebooks and pens without buying anything.

SI feel drawn to the square notebooks and metallic-colored pens attract me, even though they seem impractical. I feel drawn to the square notebooks and metallic-colored pens, even though they seem impractical.

"Attract" might be too strong a word to use here, so you can simply say "I feel drawn to...".

When I was a child, there were several small stationery stores in my neighborhood, but now they have (all) almost disappeared. When I was a child, there were several small stationery stores in my neighborhood, but now they have (all) almost disappeared.

When I was a (child), there were several small stationery stores in my neighborhood, but now they have almost disappeared. When I was a (child), there were several small stationery stores in my neighborhood, but now they have almost disappeared.

Another casual/conversational option could be to use "kid" instead of "child". For stationery, I would stick to using stationery store like you did here for the rest of the text too. But stationery shop is not wrong.

Feeling Nostalgiac for Stationery Shops 文房具屋が懐かしい Feeling Nostalgic for Stationery Shops 文房具屋が懐かしい

These days, I usually buy stationery either atin the stationery section of a supermarket, in a shop inside a station building, or online on Amazon. These days, I usually buy stationery either in the stationery section of a supermarket, in a shop inside a station building, or on Amazon.

Amazon is so common that we usually don’t bother specifying that it’s online. Perhaps that’s part of the problem!

These days, I usually buy stationery either atin the stationeroffice supply section of a supermarket, in a shop inside a station building, or online on Amazon. These days, I usually buy stationery either in the office supply section of a supermarket, in a shop inside a station building, or online on Amazon.

The term "station building" isn't common in English. Do you mean train station? In the US, there's not a specific "stationery section" - all the office supplies are grouped together. Perhaps that what you have as well?

(These days), I usually buy stationery either at the stationery section of a supermarket, in a shop inside a station building[train] station, or online on Amazon. (These days), I usually buy stationery either at the stationery section of a supermarket, in a shop inside a [train] station, or online on Amazon.

(): casual/ conversational option = Nowadays []: are you referring to a train station here?

I miss the old days, when I could wander into a stationery shop with no particular purpose and enjoy discovering new items. I miss the old days, when I could wander into a stationery shop with no particular purpose and enjoy discovering new items.

What you wrote is grammatically correct, but when I hear this spoken, there is usually a pause after “old days,” just long enough to give the listener time to conjure up memories!