I did once read an article about increased ear infections and respiritory infections in children who started swimming under 12 motnhs. But i certainly don't remember where i read it or even if it was credible information!
But at the time it was enough for me to decide to put off lessons until DD was one. That combined with the fact it is freezing here in winter when she was 6-11 months.

I took her in my mum and dad's pool at home when she was 8 weeks old though, just not public swimming pools.

She'll start lessons soon.