Full subcutaneous tissues of the brows is absolutely a sign of youth. This effect can also be mimicked by temporary filler, by fat injection, or we prefer LiveFill(R), autologous fat grafts with nontraumatized tissues placed underneath the eyebrows in a subtle fashion.
Botox helps to elevate the corners of the brow as well, although of course it is not a filler.
The interplay between the brow, the upper eyelid and the face as a whole is complex, and patients often focus on one aspect while missing others. A skilled plastic surgeon can point out the individual components and how they affect each patient's unique features.