My friends interest in these substances started at your age. The fear was so big that he tried them 7 years later for the first time. It does not hurt to read as much as you can before trying them first hand. My friend is not really experienced, but he did that first step a while ago, and it was good. Noone can decide for you. I can only tell you, that there are a lot other intense experience to be had at 18. I'm not telling you not to do it. If you get the call, you should consider answering. It's just not running away (You should do it before 2012 though  )

DMT is a tryptamine compound and vastly different to Salvia (and I guess Ketamine)...both have more dissociative properties. They are visual but also come with strange ....I mean strange sensations. DMT is different. I would say friendlier than your regular salvia trip. But I can only speak for sub breakthrough doses which are, as matter of fact - pretty impressive at times.