Has decided following the last Dev Q&A, tests have been made about armor training.
I've tested Ligth Armor, like you mentioned, with the exact same skills as your "new" character and had 1280 Health points. Within 5 minutes, changing of beasts and tweaking my acessories (items I bought to Harnquist, everything 50Q), I found a way to level up my Light Armor which was at level 17. It didn't even needed the use of healing potion at all.
So basically, it is possible and not even problematic as far as i saw. Of course it is slower then before but this is legitimate.
Like I told you in game when you made a petition about it, you need to make experiments, see which beasts suit your skills and if one big is too hard then maybe several small are better ? I will make further tests with MA and HA but so far, it's working just fine.