Of course, I mean besides Lt. JG Picard in "Tapestry":
Is it just Hollywood bias or are we to believe that officers either get promoted, get killed, or retire if their career is not advancing?
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Lt Jg Reg Barclay was (approx) 42 years of age when we meet him in TNG: Hollow Pursuits. That seems rather old for such a low rank.
Lt Jg Janice Rand was (approx) 51 years of age when she was promoted to her rank.
Ensign Alans was a technical specialist (a volcanologist).
When we meet him, he's (approx) 45 years of age.
Ensign Cheney's age isn't described in canon, but she doesn't look that young (mid-50's?)
Obviously it's a bit different for longer-lived species, but Ensign Chu'Lak was aged 77 when he was commissioned an Ensign.
And Ensign Tuvok was approx 85 years old when he rejoined Starfleet as an Ensign.