Andre the Giant, Vader, Undertaker, Kane, Henry, all those guys were effective at least til they turned 40. Not prime effective, but certainly in a way that didn't hurt their drawing power. Strowman's 34, if he has six years left do you worry much about his age?
If there's a size bias, it's that super-heavyweights tend to make it to the top faster than average sized workers, and the mileage on their bodies may hasten their demise.