Since 2000 [the reunion, then], I've changed jobs twice.
２０００年［同窓会，それ］以降，私は２度転職している
since childhood
子どものころから（◆日常的には，since one was a child）
Since his wife's death, he has not been all there.
女房が死んでから彼はどうかなってしまった
Since it's such a nice day, let's go for a walk.
すごくいい天気なので散歩に行こう
Since nobody said anything, it must be [I guess it's] okay.
だれも何も言わないってことはきっとオーケーなんだよ
Since the age of 18, I have been out on my own.
１８歳のときから自活している
Since their office was too small, they decided to move.
事務所が手狭なため，彼らは移転することにした
since then
それ以来
Since when do you smoke?
((略式))いつからタバコを吸っているの？（◆驚き・怒りを表す）
Since you asked [you're asking] (me), no.
（人に回答を迫られて）君がたずねるから答えるけど「ノー」だよ
