Can you drive airboats in GTA 6?

Yes. Game Informer confirms airboating.

Where can you go airboating in GTA 6?

In the Grassrivers, Leonida's swamp region, where Rockstar's screenshot shows one.

Game Informer's cover story confirms airboating, along with street and off-road racing and jet skiing.
Rockstar's screenshot of the Grassrivers, Leonida's swamp region, shows an airboat from above.

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01 / Activities
GTA 6 activities
29 GTA 6 activities confirmed: robberies, street races, gym, hunting, fishing, scuba, mini golf, pool, nightclubs. Plus 8 seen or probable.
02 / Activities
GTA 6 jet skiing
Jet skiing is a confirmed GTA 6 activity: Game Informer lists it, and the Extended Look shows two jet skis racing across Vice City waters at sunset.
03 / Activities
GTA 6 kayaking
Kayaking is a confirmed GTA 6 activity, per Game Informer. Lucia paddles across a Vice City marina, and a Crest Kayak waits outside Jason's safehouse.
04 / Activities
GTA 6 hunting
GTA 6 hunting is centred on Mount Kalaga National Park. Leonida has over 170 animal species, some rare or legendary, to study as in Red Dead 2.
05 / Guide
Grassrivers on the GTA 6 map

Still unknown: Whether airboating is free roam only or has races or tours.

Can you drive airboats in GTA 6?
Yes. Game Informer confirms airboating.
Where can you go airboating in GTA 6?
In the Grassrivers, Leonida's swamp region, where Rockstar's screenshot shows one.
In depth: GTA 6 Map: The 6 Regions of Leonida