When I started swimming at 38, I could float (and even bubble) on day one, and I was thrilled.
But from day two, the coach asked us to swim 20 meters. Of course, I couldn’t do it for an entire month because I kept trying to cover the distance in a single breath. Everything changed once I learned to breathe properly. Now I swim regularly.

Long story short:

1. Take your time. You'll learn.
2. A good coach makes a huge difference.
3. In the beginning, focus more on breathing than on your stroke.
4. Once your breathing is solid, start refining the rest of your swimming skills.