Most adults are in condition to surf. At the beginner level there are a few techniques that have to be learned but adults are often better learners than adolescents and young teens.
I have taught students 7 to 77 and the 77 year old got up the first time and most times after that. He was a ski guide and had athletic abilities but age is functional not chronological.
Most helpful for adults is flexibility, upper body strength, and core strength. A beginner pop up I teach reduces the need for upper body and core strength so most people can achieve standing up and riding the surfboard.
Aerobic Fitness
Aerobic fitness is helpful because paddling is tiring. Swimming is the closest match to paddling, but pulling cables at the gym is good cross training. Walking briskly and biking also help.
General leg strength can be gained at home by doing squats and lunges without weights. Core strength can be quickly built doing planks in your living room. The pop up assimilates burpies which most people learned in high school. Burpies build aerobics, legs, upper body and core.
Adults can get into condition to surf or build conditioning while learning to surf with these simple exercises.
The Surfing Pop UP
The pop up is the main technique to transition from lying on the surf board to standing up and riding. It consists of a few facets that include positioning for the wave, paddling to get in front of the wave, and then standing up.
The beginner pop up starts with putting your hands under your chest after you are in front of the wave. Then you push up and place your rear foot in the middle of the board under your butt so you can stand on it. While pushing to stand you are lifting your hands in front of you toward the beach.
At this point, the front foot is weightless and can be placed forward on the surf board in the middle of the board. It should be far enough from the nose not to push it under water, but back far enough so the board rides level. If your weight is on the back of the board, the nose will rise up and you lose the wave.
For Surf Lessons in Oceanside, see the Home Page
See my dry land and water demo video
A good video on how to catch waves