LEARNING A NEW SKILL
I think that the best age to start learning English is as soon as you’re born. But most people can not affect the way their parents teach them a language as babies. During that time, parents are responsible for the development of English that you have. In the case of a person who is from an English-speaking country, it's the norm for parents to teach their kids primarily English. In other countries, children can be taught English by their school, somewhere around the age of ten. If someone can’t speak English but wants to, the best age to start learning is however old they are now.
It’s easier to learn when you’re young, because of white matter in the brain, but even children won't learn English easily if they don’t like it. So being willing to learn is the most important thing for learning English.
I think that I’m in the automatic stage because I can communicate with it without much trouble. Sometimes I still struggle with spelling and pronunciation, but I’d count those mistakes as technical issues that don’t affect my use of English. I am still learning more every once and a while.
Learning languages is comparable to driving, playing an instrument, etc. Once you learn how to do it, you never really forget it no matter how long of a break you take from it. You might forget details or rules, but then start remembering them as you start practicing again.