To my knowledge, aged shu and sheng are more neutral, though they do carry the basic characteristic of sheng is cooling and shu is warming.
Some young sheng are more stimulative and aggressive/cooling in nature, which may cause gastric problem in the long run. The worst are the tips of early spring. They normally carry the most cooling effect. Most will find drinking some young blended sheng better than others, as there are some aged content.
Young shu are often more warming as they carried more "fire" element in them when they are "cooked"/fermented. They "fire" element gets reduced over a period of time.
The timing which you drink also influenced the result you get, as TCM believe the different parts of the body absorb stuffs at different timing. Kind of like milk if best drank before sleep as calcium is best absorbed then.
The weather and season also affects the result of what you drink. Also the body condition.
My personal experience is that body condition is supported to be cooling in nature, so shu was supposed to be best for me. But my body seems to accept young sheng better than young shu. My explanation is that Singapore is too warm.
To know more you are better off reading 本草纲目. Most of what we know are bits of pieces. Some stuffs may had been "twisted"