Tube amp biasing question---

hello all,

just wondering, my amp, a Jc Verdier Audiobloc II has to be manually biased to 18v Dc.

at the MINIMUM range of the bias pot, I still get approx 18.9v DC, at the top range of the Bias pot, i can get almost 26v dc.

my tubes are all tested in the good range.

my question....could it be my tubes are too strong?
would swapping in some weaker tubes (aged tubes) allow me to lower the bias point to reach 18v dc?