find the mistake

By the age of twelve, I learnt to swim a little.

By the age of twelve, I had learnt to swim a little

At the age of

by the age of twelve, i had learnt to swim a little

شكرا . اساتذة كتيير قالولى كدة و انا عملتها صح كدا و مدرس الفصل بيقولى عدتهالك !!!!

so easy had +pp

by the age of twelve, i had learned how to awim little

this sentence consists of past simple ------------------------------- past perfect

how to learn

Ihad learnt to swim little By the age of twelve,