My brother, who is almost 17, is EXACTLY the same. Part of it is character I think, but he definietely has more anxious tendancies than others, and some really over-the-top worries (I won't say irrational because a lot were quite rational, just really over-the-top, like your DS finding a block of land in a court!) and a counsellor really helped him. I hope you can work with him and help him, it sounds like he has an awful lot on his mind!