わかわか若々wakawakaしいshii
1.

Exhibiting traits or characteristics that convey a sense of youthfulness and vitality, often associated with energy and freshness.

2.

Appearing noticeably younger than one's actual age, suggesting a vibrant and lively demeanor.

3.

Possessing an immaturity or naivety, sometimes reflecting a lack of experience or sophistication in behavior or outlook.

Example:

その年になってもまだ彼女は若々しい少女の面影を保っていた。