Honestly? No. First of all, someone who is 18 and has never skated has to overcome something huge, which is the fear of falling. Little kids fall and bounce right back up and never think about it, and as they get older they are so used to it that it doesn't faze them at all. As basically a full grown adult, there definitely is that fear to conquer. Also, at 18 its quite likely that you are either in school or working, or both, which doesn't leave the many hours of necessary training hours that you need to make it to Worlds or the Olympics. If you are bound to a certain place because of school/work, then you may not have access to the coaching and off-ice training that you need to get to the top. I think that at 18 and over, there are just too many things that will prevent the vast majority of new skaters from becoming world class figure skaters. That doesn't mean that you can't achieve something in skating, though. At 21 you can start competing as an adult, and there are several big adult competitions out there. There's the US Adult National Championships (which I went to this year, three years after starting to skate at 22 years old), and there are even some international adult competitions.