I love swimming. I have been holding my breath underwater since weeks within my birth.
Really!  Is it natural for an infant to be able to hold their breath under water?
Yes. it is an evolutionary response to not only hold our breath, but to undertake rudimentary locomotive swimming withing weeks of birth.
That is amazing!  I imagine it must be harder to learn the older you get then, right?
I am not sure, but swimming is a very low-impact activity.
Swimming would be good for people with arthritis or bad joints than right?
Yes because our bodies are only slightly less dense than water, water supports our weight.
I will keep that in mind as I get older and will need less impactful exercise.
Higher levels of fat and saltier water will both lower the density of the body, increasing buoyancy. 
Interesting!  So I can float better in the ocean than in a pool?