When I became interested in Judaism I was 16 and was in charge of a weekly girls’ group in the protestant church in my neighbourhood. But the rest of my life wasn’t actually very religious, I didn’t pray or read the bible or believe all the bible stories literally. I was in for the people and the music.
Judaism changed my life pretty fast. I remember doing my first Shabat not even a month after I stumbled upon Judaism (hidden from my parents). There was no synagogue in my city, but I spent loads of time in a Jewish chatroom. I tried out lots of things. I turned off my computer for Shabat (more out of boredom, because the chatroom was empty). I fasted for Yom Kippur (without telling anyone, not even my parents, just to see if I could). I became a vegetarian (easier to explain than kashrut). I learned Hebrew (when I was bored at school). I memorized the Kaddish (don’t know why this prayer exactly). There was no Jewish community reachable for me, but I did what I could on my own. I didn’t want to convert at that point, I think. It was more experimentation of how crazy all of it actually was than really believing in it at the beginning.
During the same time I continued to be actively involved in my protestant community. And I subtly changed towards Judaism. When I had to tell a biblical story, I took it from the "old" testament – it has great stories, nobody really missed anything. When I had to select songs I selected those without Jesus – there are lots, nobody even noticed. In the bigger events I volunteered for the music group or the outdoor activities instead of the bible groups. The children or the pastor never knew. My fellow counselors probably suspected, because in our discussions my viewpoints became more and more synched with Judaism. One person told me I’d go to hell if I don’t believe in Jesus. But at that point I was so far away from Christianity, it didn’t matter to me at all.
Without really realizing it or planning on converting, I ended up observing many Jewish things. And it just fit! I don’t think I did anything "religiously Jewish" like rituals or praying though.