Tube preamplifier lifespan

It looks like you are looking for a particular answer or opinion that matches your already made- conclusion 

@tablejockey, Paul McGowan told you that a tubed component only lasts 20 years?

With most tube gear, you can expect a MUCH longer serviceable life than solid state gear.  Most parts can be replaced on tube equipment while many solid state gear becomes unrepairable because a chip or transistor is no longer available.  Also, tube gear has far less parts because the circuit is simple.  One of the technicians at a local shop restored a solid state receiver as a labor of love.  It took, among other things, replacing more than 200 capacitors; this would never be done as a commercial repair.  
 

My tube preamp is about 15 years old and has required no repairs nor replacement of any tubes.  Moreover, most of the parts were very old when it was built by a custom builder.  The power supply is new, but the audio circuit parts are up to 80 years old.

I'm listening to a 25 year old preamp it sounds great and works great haven't had a problem with it besides an occasionally dirty pot and changing tubes. It's a custom job so kind of a one off but tube preamps can last very long and plenty have. 

I have a Sonic Frontiers preamp built in '94 that still sounds great.   Many small signal tubes can last 10,000 hours , that's a lot of listening time.   

I've had it about 5 years and it still works flawlessly.