Deck Destruction decks in general are a great counter to Lightsworn, since good Lightsworn decks already get rid of 70% of their deck in the first few turns.
There are only 6 spaces in DL which means you have to have all other spaces filled in order to use this card. If you are in that position, then that probably means you are already winning.
You don't even need to test it actually, since it says "whose combined Levels are double the revealed monster's"
It never says "double or more", just "double. So of course having 2 Level 6 won't work to summon a Level 5 one.
Using Nekroz power can change your age temporarily, usually making you older, and "Gishki Avance" has it the hardest here lol.
Amusingly when he wears fallen beings as armor (for example, when he becomes "Nekroz of Valkyrus"), he actually de-aged. And when he becomes "Zefrasaber, Swordmaster of the Nekroz", he's a young man XD