am I too old to learn to swim...?

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I am ~40 and I never had any kind of swimming lessons. I kind of learned on my own while hanging out with buddies at a lake when I was a teenager, and then I had a friend about 6-7 year ago trying to teach me to swim better but he had a hard time with me.

I can float on my back, I can swim across the pool and back (not sure how long is it), but I am swimming very slowly, and because the way I swim is very ineffective, I also get tired very quickly.

I take my son to swimming lessons every week and I am thinking to ask if they have an adult class for people like me.