So this all started when I was re-reading CK and realized that Leoni's age was compared to Jesper's age when his mom died. It says "A child several years older than Jesper" implying that she was AT LEAST four years older than him, if not more(assuming "a couple" means 2, and "a few" means 3, therefore "several" means 4+.) Nina and Jesper are the same age in CK. They're 17. She is 18 in KoS. Leoni, being "several years" older than her, is about the same age as Adrik. Adrik is expressly stated as being 2 years younger than Zoya. Zoya and Alina are the same age. Nikolai is about 4 years older than Alina. Therefore, in KoS, King Nikolai is 18 + (4+) + 2 + 4 = at LEAST 28 years old. Most likely older bc very rarely does "several" actually mean 4.