Primogeniture is not actually unreasonable if you consider that children can range in ages say 15 to 20 years. On average the oldest is most mature and experienced. Both reasonable qualities up to certain point. If your existence depends on decision of single leader. I generally would pick the 30 year old one over 20 year old or 25 year old over 15 year old. Post 30 year old, it gets different, but to around there I would reasonably expect maturity and experience to matter.