I fancied getting a valve tester so I can pretend I know what I’m doing 
The rate at which a valve’s characteristics change tends to depend on how hard they’re working - the more the circuit stresses them, the faster they go downhill. But with small-signal valves like these I’d expect to get 10,000 hours out of them before they’re in serious trouble. Pentodes can go noisy (particularly EF86s) but I see that less often in triodes.
The extent to which matching matters depends on the circuit. Some would argue that if the circuit only works properly with very tightly matched valves then it’s a bad circuit, but there we go. Matching is a can of worms:
i) if we really do need good matching then we can select valves to get two that are close, but we can’t do anything about a valve that has two mismatched triodes inside the same glass envelope
ii) if valves really have to be tightly matched then it’s important to match them at the point at which they’ll be operating. Matching them in a tester which puts 250V on the anode and a runs current of 1mA through them won’t necessarily mean they’re still matched in a circuit which operates them at 90V and 3.5mA
iii) anyway, is the tester a high-quality one and when was it last calibrated ? With some testers it’s quite possible to learn a lot of things that aren’t true (here are the ugly facts about testers My (never complete...) Tube Tester Collection it’s a long read but a salutory one).
Just my two penn’orth of course.
VB
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Thanks for advice.