The big difference is that athletic talent peaks early. If your human material is going to be used up and tossed aside by age 35 (at most) it makes sense to try and get them early. See recruiting practices (and training methods) for female gymnasts. Vs, say, philosophers. Or mathematicians.
People rarely get Nobel prizes in the sciences or the Fields medal in math for work done in their 50s and 60s, so the age profiles of athletic and intellectual talent have some resemblance. Fluid intelligence peaks in the early 20s, just as athletic ability does. A good part of a scientist's research potential is used up by age 40, which is why getting tenure by then takes on great importance for individual scientists. One reason academic acceleration of the gifted is important is that it may increase the research "lifespan" by a large fraction. If one's best research is done by age 40, someone whose research career starts at 20 has 33% more peak years than a researcher whose career starts at 25.
