YOU SAID:

my friends are so mature, they are so cool

INTO JAPANESE

私の友達はとても成熟していて、とてもクールです

BACK INTO ENGLISH

my friend is so mature and so cool

INTO JAPANESE

私の友達はとても大人でとてもクールです

BACK INTO ENGLISH

my friends are very mature and very cool

INTO JAPANESE

私の友達はとても大人でとてもクールです

BACK INTO ENGLISH

my friends are very mature and very cool