A racing bike used for thousands and thousands of miles by a hammering profesional will lose it's liveliness over time. A bike riden, even for many years, by a sports/exersize oriented amateur probably wouldn't suffer much metal fatigue. Assuming a steel bike of course. Aluminum say, has much less metal fatigue resistance, so maybe over time with a heavy strong rider, who knows? Never-the-less, I doubt you'll have any problems. I have a 1974 Austro-Daimler Vent Noir that still feels more or less just as "lively" as when I bought it way back when.
Enjoy it, ride it, love it!