Lifespan of a quality solid state amplifier?

Bifwynne, 6 months is nothing. You can safely plug it in. Caps go bad after at least few years unpowered.

I get the picture. Well-made piece should last at least for 50 years with proper use and care and with maybe some not very big repaires every 15 years or so. That's pretty good. And tube amp should last 150 years, I would guess.

Kijanki, can I power up the amp without a load or input signal? I've heard that it's best to have a load with tube amps. Different beasts of course, still better to ask.

Bifwynne, No input signal is OK. Tube amps need load, SS amps don't.

SS amp might fail when input signal is present and output shorted (overcurrent). I've heard that some poorly designed class D amps might go into oscillation without load but likely will survive that.

Tube amp might fail when input is present and output is open (overvoltage). It might even happen without input signal if amp goes into oscillation.

I increase volume slowly, at first, making sure I hear the sound from both channels. It is good habit, IMHO, since things tend to get shorted or disconnected between listening sessions.

My personal experience of owning SS gear for many years is that leaving gear on 24/7 is silly, wasteful, completely unnecessary, tawdry, untoward, and pretty much unjustified by any meaningful data ...the wasted juice far exceeds the cost of any "premature ageing" of a component due to turning it on and off.