老当益壮

lǎo dāng yì zhuàng

old but vigorous (idiom); hale and hearty despite the years

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

当

dāng

to be

益

yì

benefit

壮

zhuàng

to strengthen