I worked as a messenger boy even though I hadn’t had any experience. (the poster)

  I worked as a messenger boy, even though I have never had any experience.

(My little change in the above sentence, for the time)

   For I read in this novel The Undomestic Godess the phrase: "I have never failed an interview in my life."  So, I think this could be the same verb tense, once both of them are informing about something that happened long ago, perhaps in the similar circumstances.    But, it´s open to peer comment, and I, myself will study it a little more, I am indeed going "by hear" now.     I will try the books soon, to confirm.

I worked as a messenger boy even though I didn't have any experience. (Johannes)

  Makes tons of sense, Johannes, I would go there at first sight.

  Same as above; I will try stabilish some difference between the two, if there is any.

  You know, verb tenses are my Achiles heel.

   But, I don´t know why, but I think they can be used.  Only that is slight difference in

use (that difference will be better explained by teachers around, or as sooner as I can).

   I´ll be back He Man...!

   In fact, the part  in wich there is the bit  "...though I hadn’t had any experience." seems  unusual, to say the least.   But, I need more study.  I want not fell off the tightrope by being hasty!

   See you later, PP.