Psalm 148:12, "both young men and maidens; old men and children:" is a poetic expression emphasizing the universality of praise to God. It means that everyone, regardless of age or gender, should praise God.

Here's a breakdown:

"Young men and maidens": This represents the youth, the strong, those full of vitality and potential.
"Old men and children": This represents the elderly, full of wisdom and experience, and the very young, full of innocence and promise.

The verse deliberately includes all stages of life to underscore the point that praising God is not limited to a specific age group or social class. It's a universal duty and privilege for all of humanity.

The significance can be interpreted as follows:

Inclusivity: God's call to praise extends to everyone in the community. No one is exempt.
Intergenerational Worship: It emphasizes the importance of all generations worshiping together. The young learn from the old, and the old are encouraged by the young.
Wholeness: By including all demographics, the verse paints a picture of a complete and unified chorus of praise rising to God.

In essence, this verse is a powerful reminder that praising God is a fundamental aspect of human existence, and it's a responsibility and a joy that should be embraced by all, regardless of age or gender.