[1.2.340] Full Lionheart Castle

The skill being level 16 has to do with it's description tho.
Soul Diver:소환된 미하일이 소울의 힘을 땅으로 스며들게 하여 다수의 적을 4번 연속 공격한다. 레벨 10 오를때 마다 스킬레벨이 1 상승한다.
Bla bla bla bla uses MP to attack a monster 4 times with the strength of your soul bla bla bla. Once each 10 levels, the skill level rises by 1.

Basically, it's exactly like the blessing skill. Once your character levels up 10 times, you get one point into that skill. They're just upgraded versions of the Cygnus skills.Since the max level of the skill is 16, and you gain 1 point per 10 levels, this means their max level is 160.

If you look under Quests you can find "60 레벨 스킬지급" which means "Level 60 Skill Allowance" and its quest description translates into "You gained 1 level in UA skills" so its most likely that you get the first level in UA skill once it is created and first level up at level 60 and every 10 levels there after
until you reach level 200 where the UA skill would reach max level at 16 as well.

and you can also see that same Quest exists every 10 levels until 200.