Unless you really must have gentoo, ubuntu and redhat on thier sites list many PC based laptops that are known good with thier os'.
If you don't want to pay for red hat cent os is the same thing so I imagine the list stll applies.
In my experience its not boot loading that is an issue with linux on physical systems....its having everything work on the physical system in the OS. Wireless nics for example...I saw ubuntu early have it work out the box in one release then break it in the next and it need some work to get running. Laptop was not on list so I made my own adventure there lol.
Or you could run linux in virtual with with the air. Avoids boot loader issues. Not sure of other vm offerings but I know parallels in vm configs gives the option to shift more resources to guest vm than host mac os. If looking to have the vm the "primary" system its possible to an extent.
^^ people who are interested in Gentoo are generally not interested in RH/Cent/Scientific nor ubuntu or it's derivatives. The loss of control and the out of date packages make them to say the least unappealing, then there is package managers if he was running an enterprise desktop SLED or RHEL would be perfect but that doesn't seem to be the case here.
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The Latitude line is well supported, then there is system 76.