Lieven asked Okrand about this at qepHom'a' 2016, and posted about it to the mailing list, although I'm not sure he got around to posting it to qephom.de or anywhere.
So "this event happened when I was forty" would be qaStaHvIS DISwIj loSmaHDIch,
In this conversation Okrand gives ordinal numbers for age, beginning with {DIS paghDIch} for the year following birth. This conflicts with the way I thought Klingon birthdays were numbered: {qoS wa'DIch} for the actual day that someone is born, {qoS cha'DIch} for its first anniversary, etc.. It would hardly make sense for the zeroth year to start on the first birthday and end on the second, but perhaps I'm mistaken about this birthday numbering, since I can't find a source for it.