* Dragon Ball Z: In Dragon Ball Z, Dr. Briefs is established as being in his late 50s to early 60s. He's shown to be a successful scientist who's already established his career and has a grown-up daughter, Bulma.
* Dragon Ball GT: Dragon Ball GT takes place some years after the events of Dragon Ball Z. Given that time has passed, Dr. Briefs would likely be older, possibly in his late 60s or even early 70s.
It's important to remember that Dragon Ball GT is not considered canon by the creator of Dragon Ball, Akira Toriyama, so the timeline and age of characters might not be exactly consistent with the main series.