Well, the language in "Tuo kaunis Kalervon poika..." (that beautiful Kalervo's son) is not that old at all, I'd say. To a (modern) Finn it sounds archaic because it is rather a mixture of Karelian and Finnish – I'd place it somewhere between Vuokkiniemi & Suomussalmi – and besides, I am pretty sure that the person who has "given" it, must have read Kalevala as well.
I'll try to spare some time to give a translation of that "fragment" of Kullervo's tale (even though his name is not once mentioned in it!)

AKS