na-adjective, noun which may take the genitive case particle 'no', noun
Describes a person or thing as being young or having youthful qualities. Often used in literary or slightly formal contexts.
The two young people were chatting happily in the park.
He started a company at a young age.
Compound of 年 (toshi, 'year, age') and 若 (waka, 'young'). The reading としわか is a straightforward combination of the two elements.