I don't even know if I coslept as a baby/toddler or not, although I was always welcome to come in when I had bad dreams, but I did often co-sleep with my mom as a teenager when my dad was gone to work. It really helped with my insomnia. It was comforting to me and I think she might have appreciated the company too. I had always shared a big room with my sister, but after my sister moved out, it would be just my mom and me for the winters when my dad was away. So we teamed up to sleep. Besides, our house was cold! Anyway, we probably never mentioned it to anyone, because the topic never came up, but I can't imagine anyone thinking it was weird. Which makes me think that people's perception of extended co-sleeping is colored by the idea of sexuality (since it comes up more often that it's "weird" when the parent and child are opposite sexes). Which is a real shame. Some people, like myself, just really like sleeping beside someone - for a while it was my old dog, when my husband would be away. Or my best friend, because she also likes someone to sleep near.
Anyway, I think it's totally normal to want to sleep next to someone at ANY age, and personally would be pretty tempted, if someone tried to insinuate otherwise, to make them feel like the weirdo. But I'm kind of subversive like that . . .