What age should a Kid start swim lessons?
There is not a specific age for swimming lessons, typically lessons start around the age of 4.
We have an excellent coach who's a high school swim team coach as well as a park and rec coach. The varsity high school team has been state champions several years a row; she's that good. She has a class for infants, and teaches them to hold their breath and float to a ladder if they should fall into a pool. This helps them not be afraid of the water as they get older too.
At our YMCA we do a parent tot with parents and their children in the pool at the same time from the age of 6 weeks to 3 years. At three years the child then starts swim lessons. In the parent tot classes we learn about water safety and really just getting a child comfortable with water but we do progress to them jumping off the wall and going all the way under, blowing bubbles etc. as appropriate by age. Then, by the age of 3 they really are ready to start to learn to swim. I also teach an adult learn to swim class. Don't wait too long, teaching adults to swim is rather challenging as 90% of it at that age is mental.
Most classes start with mom or dad at 6 months old, and typically let them be in class on their own around 3 or 4 years old. But if you can, get them in the water as soon as possible! I've read that getting them in the water as soon after birth is best, as to symbolize being in the womb.
It is great to get your children familiar with water as soon as possible. Some facilities will offer "Mommy+Baby" classes with children as little as 6 months old. Private lessons can be given for kids a bit older, so they can can begin to develop the skills necessary to swim on their own. Group or private lessons are beneficial for the children, so that they can also understand how to be safe in and around water. Some competitive swimmers can begin at the young age of 5, but swimming is a progression that can be taught at any age.
I have three of my own (8, 6, 4) and we have had them in the water since before they could walk. However, the older two were not swimming independently until recently, when we chose to utilize a summer swim program- again.
Each of my kids participated in a 'learn to swim' program when they were about 2yo and were deathly afraid of putting their heads under water. Now that they are older and the youngest sees the older ones swimming 25+ meters I am sure they will all be swimming independently by the end of this calendar year.
So, to answer your question about what age to start lessons, any age is great. There are 3-4 year olds winning medals for 1st, 2nd, and 3rd place in 25 meter swim meets (multiple strokes too).
I teach private lessons and I usually don't teach until they are at least 4 years old. If they are younger than 4 they are typically too stubborn or scared of the water and I feel it is a waste of the parents' money since we cannot do much. Instead, I suggest to the parents to teach their kids how to blow bubbles in the bathtub (without their mouth being wide open, as well as teaching them that you can not breathe underwater), as well as take their kids swimming with them so that they can get used to the water. Then when they are of age to learn from me, they can actually learn a lot more than just blowing bubbles, they will be a better swimmer, and they will have saved some money in swim lessons. It's a win for everybody.
There is not one right answer to this question. There are so many variables. In general, the younger we are when we learn something, the more proficient we become lifelong.
That said, the very young child must find the activity constantly enjoyable. It requires a very patient and non-pushy teacher and parent.