Alas, science offers no cure aside from reading glasses or bifocals. Laser eye surgery can't restore the lenses' flexibility. By getting rid of their nearsightedness, they've also guaranteed that they'll later need reading glasses. Bifocals may be the most obvious harbinger of aging, but other, more subtle signs have larger significance. Starting in the 20s, the body's ability to use oxygen to power physical activity drops by about 1 percent a year.
Muscles begin to lose mass, and the body's metabolic rate slows.
In the 30s, adrenal hormone and estrogen levels start creeping downward. Much the same thing happens in the brain. The declines are most obvious in processing speed, which decreases by about 1 percent a year from age 25 on. The ability to cope with novel information deteriorates, too, by about half a percent a year. That probably stems from changes in the brain, including loss of neurons and a reduction in neurotransmitting chemicals.