Given the newer wi-fi hardware can support higher data transfer speeds,
what kind of wireless router or base station do you use?
Or are you able to access a cellular network, & still have issues, there?
If you find there are several nearby private wi-fi users whose base station
or internet access points are on the same channel you set yours on, change
the channel of your base station. You may choose to ignore other networks.
There are a few good articles in Apple Support online, in several places,
about wi-fi concerns, connectivity, base stations, AirPort, & so on. Also
in the Help viewer in your computer, you can access this kind of info.
Hopefully you can locate the correct information relating to your circumstance
and the configuration of hardware/software regarding the MacBook/Air.
Good luck & happy computing!