Basic Trope: Someone who was the best fails to keep their skills polished.
Straight: Alice the computer programmer's mentor Bob decides to retire because he can't keep up with the latest advances in computing.
Exaggerated: Alice's friend Bob drops out of medical school because he can't keep up with the changes in medicine that occur while he's still studying it.
Downplayed: Bob is late to adopt new techniques, although he's competent and gets around to them eventually.
Justified: There has just been a massive breakthrough in the field of computer science, making much of what was relevant only a year ago worthless.
Inverted: Alice gives up on programming despite the tutelage of Bob because she can't grasp the basics.
Subverted: It turns out that a lot of older systems still need people with the apparently "obsolete" skills to help upgrade them. Bob has a few more years of work to do yet.
Double Subverted: Once everything's been upgraded to the new standard or scrapped, Bob retires at last.
Parodied: Bob is shown using Steampunk style computers and considers the fact that he took Alice on despite her being female "absolutely astounding for one of her delicate sex".
Zig Zagged: Bob's knowledge of modern computers seems to vary from episode to episode.
Averted: Everyone who works with computers is assumed to know what they need to know.
Enforced: They need a way to write Bob out, or at least make sure he can't solve all of Alice's problems for her.
Lampshaded: "Sorry Alice, but my role on this team is 'Affable mentor figure'. I can't learn anything new without undermining the entire dynamic."
Exploited: Bob is sick of working at Trope Co., so he fails to learn anything new after a certain point and becomes steadily less competent. This forces the company to fire him and give him a generous severance package while leaving him free to work elsewhere (as soon as he spends a few weeks studying, of course).
Defied: Bob constantly reads journals on new advances in computing, attends seminars and even retakes his degree at one point so he always stays on top of things.
Discussed: "Yeah, there's a lot of unemployed COBOL programmers out there. That's what you get for not jumping on the C family wagon."
Conversed: "Hey, are you one of those Cool Old Guys who doesn't know anything new but still outworks everyone else?"
Deconstructed: Bob's inability to understand modern systems leads to a lack of protection from modern problems. He has his life's savings stolen because even though he subscribes the idea of using online banking, he doesn't understand how to keep his details safe.
Reconstructed: However he uses a bit of good old fashioned (computer based) detective work, combined with some old friends in the old guard of the hacking community to track down the thieves, recovering both his money and claiming a reward for assisting in their capture.
Played For Laughs: Bob chews out Alice for not carrying a wrench in her repair kit and tries to fix monitors by squirting them with oil in case "something's stuck".
Played For Drama: Bob's at risk of being fired, costing Alice her mentor.
Go back to [~Obsolete Mentor~]...I mean Obsolete Mentor...damn new fangled custom titles, I miss the pTitle system...