Board Thread:Oblivion/@comment-68.5.70.202-20180325073846/@comment-76.180.143.192-20180804143709

If I may dispute,

It is rather widely accepted that Lucien had joined the Dark Brotherhood at an extremely young age, by which I mean under 18. (Note: I couldn't find the actual quotes or in-game information.)

So, we could reason that he is, in fact, in his 30s, but he has been in the Brotherhood for decades due to his young recruitment age.