there many people that "stealth" or "blacktop" in and around beach cities and enjoy their days by the beach. so depending on what you mean by live at the beach, ya it is possible.
i have a friend, young retirement aged that lives in a minivan in north west oregon. for the most part she spends most of her free time at one of the local beach parks. then at the end of the day she heads back into town to find a spot to sleep for the night. she also has a few friends in the general area where she might spend some time and some days are spent doing city things. some times she does have to drive a half hour or more from the beach to get to a parking lot or area she feels comfortable staying over in.
i also have a friend that travels alot, all over in a class B motorhome, alot of the time he does what he calls "blacktopping". he spends all day down at the beach or doing what he wants. then heads up into towns and neighborhoods to sleep parked on the street. if he rolls in fairly late and just parks and goes right to sleep. then as soon as he gets up in the morning just drives away to some park or other location to have breakfast and start the day he doesnt have any problems. he does not do that as his sole means of living. i think he has a sticks and bricks but travels extensively. when there are campsites available where wants, like right on the beach at the campground in brookings oregon, he will get a space for a few days. but when in places campgrounds are sparse/full/or rediculously expensive. thats when he "blacktops" to be able to be where he wants to be
you can do it, it take some knowledge/experience and the right attitude, but it can be done