Actually when I mentioned training age, I was referring not to your actual age, but to your estimation of your current status as a lifter...novice vs intermediate vs advanced...as roughly
dictated by how many years of solid, intelligent training you have under your belt (among other things, of course). Doesn't have to be precise, but it can help give us a better idea of what may or may not be viable options to employ in the pursuit of continued size and strength gains.
As for volume tolerance, that can be hard to pin down...it's highly individual, can change over time due to many factors both related and unrelated to training, and can be hard to separate from other particulars of your current training program (intensity, rest periods, frequency, etc.) But in general if you're feeling reasonably rested and recovered when it comes to training particular muscle groups the next time around, you're probably tolerating the volume you're doing well enough insofar as it represents just one part of your overall program.
As to whether you'd want to increase volume when you're feeling recovered, it depends. Really the answer would be to do so only if and when you need to (in order to keep progressing). I can't say it any better than Lyle himself, so I'll quote from one of his free articles. This pertains to prematurely employing more advanced training methodology (including higher volume) than one needs to at any particular point in his or her career:
So for your benching example...if you're feeling recovered and you're progressing with the three sets, keep at it. If progress stalls but you're still feeling fine and recovered, then consider adding that additional set as one possible way to spur further progress. If progress stalls and you're feeling burnt out and run down, consider a deload of some sort or some other manner of temporary reduction in intensity and/or volume.
By the way, the quote of Lyle's is from Beginning Weight Training Part 1 (https://www.bodyrecomposition.com/mu...g-part-1.html/
) If you haven't been over there to browse the free articles he's got posted, I'd highly suggest doing so. There aren't many places you can go to score free gold, but that's one of them.