<p>I am going to have to agree with Mollie here. Grad school (in physics or in bio) is all about output and quality of work, no one is going to give you points for getting in early or being young. Might as well wait until you’re more ready to take advantage of the opportunity. Believe it or not, even at the ripe age of 22, plans will change, doubts will surface, and a little bit of extra maturity can go a long way in securing some long term happiness (this is of course, what my 29 year old physics grad student friend tells me- who went straight to grad school from undergrad, did 3 unhappy years, took 2 years off, then switched into theory and has had 3 happy years and is now graduating with his PhD, and yes, he graduated college at 20).</p>