Does equipment get old?

I ask this question not in the metaphysical sense (that we get tired of it) or in the sense of equipment becoming technologically obsolete. Instead, I ask whether amplifiers and preamps (SS or tube but my particular case is tube) get so "old" that they no longer work the way they were meant to. This may sound silly (the other side of "breaking in" cables?) but can the physical implementation of circuits (solder joints, internal wire insulation, capacitors, etc - but not counting the fact that tubes ear out) get "too old"?

My gut says I'm fine (thinking about purchasing a 15yr old tube preamp) but I thought I'd check. Thanks, Travis