Young people, full of vigor and fire, dare to challenge authority.
Tips
memory
Break it down: 血气 (blood and energy — life force) + 方刚 (just now strong — at peak strength). Together: your blood and energy are at maximum strength — the fire of youth. It can be said admiringly or as a gentle warning about impetuousness.
usage
血气方刚 describes young people whose passion and energy haven't yet been tempered by experience. It's not purely negative — it acknowledges vitality — but often implies a lack of restraint. Contrast with 老成持重 (mature and steady).