Your technician is correct and there are 2 stages to the system.
As a vehicle ages the systems wear naturally and things are not as smooth/quiet/soft/hard as they were when new. (power steering pressure switch in this case)
Sensors start getting electrically "soft" reaching their tolerances so they are not as responsive as they use to be.
Valves & solenoids get partially plugged or don't extend their full travel distance. (Power steering pressure switch orifice opening)
Hoses expand increasing volume and decreasing pressure.(Your pump only produces 'x' pounds of pressure when idling and as it increases speed with engine rpm's, there is a MAX amount of pressure it produces)
Pumps wear and don't produce the pressure and/or volume that they used too.
To every vehicle, there is a wear factor that comes into play.
The scheduled maintenance is important and will help EXTEND the life of components but do not RESTORE them to "like new" condition.
What you are going to notice first as the system wears BEYOND tolerance is parking lot maneuvers, the steering will be harder to turn (But this is such a gradual process that 90% of people don't notice because they get use to it)
So in reply to your original question - your technician is probably correct and it is a normally wearing part.
He's "Johnny On The Spot" and has driven your car and compared it to others that he has driven over the years.
That fact that this only happens when Increasing rpm's, support this conclusion.
If there was a steering failure - it would most likely be "All The Time"
I hope this information helps you with your recently acquired vehicle.