Responses
if we look at the timeline with his nephew being 13, it means that he's at the very least 27yo bc he first at 13 and even if his sister married and had a kid as soon as he went to war, which is unlikely, his nephew would've been born when he was 14yo. so id say more like late twenties to mid thirties
i think their age gap is not more than 10 years because i think the war didnt take more than 3 years to end after meeting the previous captain of the first order. sigmund is probably in his mid to late twenties and brunhild was probably already an 18-20 year old man when they met in person after brunhild graduated. but idk they didnt specify anything.