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A quick Google reveals that becoming a solicitor or barrister in England requires a sequence of studies and apprenticeship which takes several years to complete post-bachelor’s degree, even for those who studied “law” in college. Again, I suspect that similar systems are in place in the rest of the “first world.”</p>
<p>The Constitution’s framers didn’t have to do neuroimaging to observe the difference in judgment between 20 year olds and older people. It’s a readily observable fact of life - to people over 35, anyway. 
As much as you might (understandably) not like it, there’s a valid reason for minimum age requirements (both express and functional) for being granted authority to perform various functions. And those minimums are based on experience and trade-offs, even if they may not be entirely “fair” to each individual. Some people can handle alcohol when they’re 16, others never can. But the minimum drinking age is 21 for everyone. </p>
<p>And the de facto minimum lawyering age is about 25, give or take. You may not like it, but it’s the product of many years of experience.</p>