返老还童

1. • to recover one's youthful vigor
2. • to feel rejuvenated (idiom)

Character by character

• 返(fǎn)return
• 老(lǎo)prefix used before the surname of a person or a numeral indicating the order of birth of the children in a family or to indicate affection or familiarity
• 还(huán)give back
• 童(tóng)surname Tong