Redditor EmpressK researched the ages of the cast members of every Star Trek series at the time that they were launched. You can view them all here. Redditor gildedheart did some number crunching to come up with the average age of members on each of the different shows:
The original series - 36
The Next Generation - 33
Deep Space Nine - 36
Voyager - 35
Enterprise - 34
The 2009 reboot - 32
EmpressK did make one mistake: she identifies Cirroc Lofton (Jake Sisko) as 18 when he was actually 14 when the series Deep Space Nine premiered. He was the youngest cast member of any series. The oldest was René Auberjonois, who played Odo on Deep Space Nine.
-via Geek X Girls
The only one that's surprising is Scotty (James Doohan). In the original series in its original run, we knew Bones was older than the rest of the crew, but assumed Scotty was in the range of everyone else. I got to meet Doohan about twenty years later, when he was approaching 70, but passed for ten years younger easily.
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