What job did Sebastian/Jeremy do? And why did he also want to commit suicide when he turns 40?

And in what ways was he so rich? How come also at one point, and in as early as 1993, he was talking on a mobile phone in his car and why IN FRENCH (how did he also learn French?) and what was the deal with his losing £30,000, how did whoever was on the end of that phone line ended costing him that?

Also - besides him being a psychopath guilt of criminal offenses too and downright gravely serious ones at that, why did he say he want to commit suicide on his 40th birthday? Even if he says he doesn't want to get old (but why does it matter to him so much?), 50 or 60 even isn't exactly OLD, let alone anything a little over 40?

With him also being rich and whatnot, and also claiming at one point that he enjoys life, why end if when turn 40? Wouldn't he also want to enjoy life's luxuries and what not? Or was it also his guilt coming in and also a desire to escape police arrest for all the crimes he committed, hence wanting to terminate his life at certain point?

Anyone know, thanks.