young couple
Refers to a married couple who are young in age, or sometimes to a newlywed couple.
The young couple who moved in next door are very pleasant.
That young couple goes jogging together every morning.
夫婦 is the general term for 'married couple', without the age nuance.
老夫婦 describes a married couple who are both elderly, while 若夫婦 refers to a young married couple.
Compound of 若 (waka, 'young') and 夫婦 (fūfu, 'married couple').