My longest SI lasts now for 20 years and my life turns around it. From childhood I kept my passion for cats, but I do not collect books anymore and know everything by heart or collect porcelain cats (but I still have my childhood-collection, but in a box). I am still fascinated by planes a lot, but I do not collect items anymore. One of my earliest SI were baby buggies, because I loved the shape of it and the chrome frame and the spinning chrome wheels (I got attentive to it age 3) and I was cutting them out from magazines and collected them and being older I visited daily a warehouse, where I would spent a couple hours to watch, touch and smell them. I was the "weird silent girl" watching the baby buggies, but people didn't interfere. (I still get a fuzzy feeling, when I goggle "baby buggies from the 80th).
Now there are some obsessions coming and going, but I am still into my 20-year-SI in a way, so they are side-obsessions, though I enjoy them, but they don't have this attraction like my strong SI.
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English is not my native language, so I will very likely do mistakes in writing or understanding. My edits are due to corrections of mistakes, which I sometimes recognize just after submitting a text.