MATURE - [adjective] fully grown and developed; being like an adult
Examples of use
He's only 15, but his mature approach to life is unbelievable.
When she left home to study in a foreign country she became more mature than I've ever expected.
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English speaking practise
Remember that if you don't use that word in English conversations or writing you'll forget it in a short time. So the best thing you can do to learn this word is just trying to use it in speaking or writing. Remember also that practise is the key to fluent english speaking.
You can always find a partner, who would also like to improve his/her