Hi there! Congratulations on your new bird! She's very cute.
We can't determine her exact age for you, but if you can find out whether she's gone through her first moult yet you might get a slightly better clue on her age. As a general rule, the younger the better, though ultimately how easy she will be to tame will depend on the individual bird and your approach. Do read the sticky threads on taming and bonding (and the other sticky threads too!) Good luck!