>>283492297
>>283492311
It's about the vibe of each character, Katakuri and Shamrock are older because they look more reserved and generally act composed so they're aimed at the type of fangirl who loves older men and wants to be spoiled by them.

In contrast, Killingham looks like a punk and acts like a brat. He obviously has more of a spoiled and rich delinquent vibe to him so Oda is very likely going to make him in his 20s.