Originally Posted by
Steve M1911A1
Any full-size, all-steel handgun in 9mm or .45 ACP would be appropriate for a 13-year-old, assuming access to very-high-quality, professional instruction.
However, your best bet would more likely be a Ruger .22 rimfire semi-auto. If you can find a clean, gently-used one, it would also be comparatively inexpensive.
The only bad thing about them is that they are extremely difficult to take apart. But the good part is that, using modern, decent-quality ammunition, you do not have to take it apart for cleaning, at least not very often.
The Ruger semi-auto .22 is reliable, easy to handle, and easy to shoot.
Bonus: Your nine-year-old can handle this gun too.