I have all 4, and thankfully they're straight and healthy. I read an article a few years ago in a magazine (Smithsonian, maybe? not sure) that said, IIRC, fewer than 5 percent of people get all 4 wisdom teeth that emerge fully and straight and don't get impacted (blocked and stuck by the other teeth). I didn't know it was that rare. The article was about "extra" body parts, like wisdom teeth, appendices, extra ribs.
Mine came in when I was 17-18. Some people just don't have them, and I know many who do have problems with not having enough room for them. Maybe one of the dentists here will chime in. I'll try to remember to ask my dentist next time approximately how many of his patients have wisdom teeth. I find it interesting, because I see the prevalence of problems with them to be linked to nutritional decline in our society through the last several generations causing most people to not have dental arches with adequate room for all the teeth. I wonder what the archaeological record shows about wisdom teeth. Did it used to be normal to have all of them with no problems?