just a heads up, I started 5 death knights, because I could. Two of them were still RaF'ed, the other three were not.
When I got out of the DK starting, the three not RaF'ed were the expected 57.75, the two that were RaF'ed were 60.5

As to making a DK and granting 20+ levels. If it IS possible I would not recommend doing so. Or at least not more then once (delete the DK make a new one and do it again) This would almost definitely be considered an exploit and put you on a very bad radar to be on.