Is age bad for solid state amps?

Yes, but probably not a worry for the age of the amps your considering, and they usually can be refurbished, especially with an established brand like ARC.

Nelson Pass re: the Pass Aleph O's:"...The amplifier does not need any maintenance. While the design in conservative, this is a hard running amplifier, as single ended Class A is the lease efficient operating mode. In fifteen years the electrolytic power supply capacitors will get old. Depending on usage, you will begin to have semi-conductor and other failures between 10 and 50 years after date of manufacture. Later, the sun will cool to a white dwarf, and after that the universe will experience heat death..."

I think it's fair to say that the Audio Research amp your considering will not be as "hard running" as Nelson's single ended Class A design.

Once again Kijanki makes a good post. While most anything can ultimately fail, all but the very first transistors introduced many decades ago, have proven themsleves to be extremely sturdy devices.

Transistors can be replaced. If matching transistors are unavailable, often times sets of different transistors can be retrofitted. Though this would probably be a relatively expensive procedure, one would have to consider what the costs would be compared to the much more likely need for frequent tube replacements over a similar time span. Furthermore, the quality of new tube replacements are somewhat suspect, which is evidenced by the ever escalating costs and decreasing availability of of NOS tubes. The likelihood that such a problem will occur with transistors in the realistic need/use of a ss amp is extremely low.