note that nba rookies who debuted at age 27 and above were actually superstars in other pro leagues and that the delay was not entirely because they were late bloomers or had to develop first. in most cases it was because these players had huge contracts that are way beyond the allowed buyout terms for nba teams. that's why pablo p had to wait till he was 35 years old to get to the nba.
oh and i honestly don't get the wait till 27 or 28 argument, logic dictates that the lesser risk timing to sign kai is "now" since his valuation is still low (being an undrafted player) plus he's relatively young enough to be molded and developed by an nba team. a 27-28 year old veteran would have more power to ask for not only a guaranteed contract but one that has higher monetary value.
in the end its really just about the talent - the nba couldn't care less if you're from timbuktu, myanmar, whatever letter of the alphabet you identify with, a knucklehead, an addict, a racist, a wannabe thug, a criminal etc. as long as you can play well enough to justify the excess baggage that comes with you, they will sign you to a contract.