I’m not certain of the years but 2015 for the F150 and 2016 for the F250 and larger were the first years for aluminum body’s. I have a 2017 F150 and live in Illinois, which gets a lot of salt on the roads.
My opinion is in theory the body can corrode but I think that will be a very rare thing. On mine I see no problems with the body but other components will still rust. For example the running board brackets on mine get chips from rocks and I could see in the future where they will rust. I have had a Dodge and Chevy pickups that had or were going to rust out. I think the aluminum body benefits far outweigh any downside.