Reported service life spans 30 to 50 years, which is wide enough to be nearly useless as a prediction — and that gap is largely where maintenance lives.
Most seawall maintenance advice is about the wall. The more useful version is about water: where it gets in, whether it can get out, and what it takes with it when it leaves.
Maintenance as an obligation
In several Florida jurisdictions the condition of a private seawall is not purely a private matter. The triggers tend to be observable from outside your property — tidal water crossing onto a neighbour’s land, or overtopping — which means enforcement does not require anyone to inspect your wall first.