In most states at 16 years old you can only get a limited license due to the graduated driver's license laws. There is required supervised driving time and a variety of restrictions on when, and with whom, you can drive. Can we try this with guns? In many cases there is a mandatory waiting period during which you have only a Learner's Permit. For a DL you do generally need at least a limited physical exam--see previous link and note that at a minimum there will be eyesight restrictions. (In NYS I generally had to read an optometrist's chart to get my DL issued or renewed.) Certainly it is the case that there are age-based restrictions.
But the big thing is you have to take a safety knowledge test and a practical test. Can we get that for guns?
Sure. Can we get an IQ test and photo ID for voting?