At the age of 21 Taylor was the CHB for the reigning premier so it's a bit rough to count him out for not being 80 days younger...
If your initial question were what defenders are getting the same numbers as him you'd be right, but you asked "Which of the current crop of KPD started out as one-on-one defenders at that age?" and I gave you the names of three players that were holding down KPD roles at 21.
If you want to shift the goalposts to a numbers based comparison in a defensive role I'll provide different names with Langdon, L Ryan, Burton and Scharenberg all offering similar numbers in the mid sized defender role. Hell look at Sicily who'd never played a defensive minute in his life until round 12 this year then averages 24p, 9m, 4.5R50's and 1.6I50's in the last 10 matches of the season in an intercept defensive role.
You are clearly correct that he's well advanced for his age, but that doesn't mean he compares favourably in a role he has no exposure in moving forward. The role we would need him to fill. What do you see in his game that will translate as a KPD aside from physique and past performance in a third tall role?
1. Facts are facts unfortunately. Lever at 20/21 played 20 games, Taylor at 20/21 played zero games.
2. Lever played in a premiership at age
21. Harry Taylor played in the Cats 2009 premiership aged
23, albeit with one of the best backlines of all time.
3. Taylor is hardly renowned as a clamp and certainly not fast. I'd wager he's slower than Lever which makes it a doubly odd comparison
4. I suspect you focused on Taylor because every other KP player you mentioned is pantsed by Lever at the same age
5. That you compare Scharenberg to Lever has you repeating the same mistakes again. Langdon's numbers are comparable to Levers but I think if you took the view on the main board that Lever and Langdon are comparable, I think we know what the response would be from the people with eyeballs. And rightly so.
6. I'm not pigeon holing him as a player, quite the opposite, so you might have to argue with yourself about that
To summarise, he's a terrific young player ahead of the curve. I think he can play one-on-one if needed but he's better utilised as a loose man setting up play. You don't get the surgeon chopping wood.