An unimpressionable mind.    From Wordnet, Princeton University. 

Adjective : an impressionable youngster.    From Dictionary.com. 

Once more he attacked the good-humoured but unimpressionable Lord.    From Wordnik.com.  [Little Memoirs of the Nineteenth Century] Reference

He was bright as a diamond, and as cutting, and also as unimpressionable.    From Wordnik.com.  [The Warden] Reference

She had the hard, staring, observant and unimpressionable eyes of a cockatoo.    From Wordnik.com.  [Lippincott's Magazine of Popular Literature and Science Volume 12, No. 28, July, 1873] Reference

Hallie Ordway leaned forward and twinkled at un unimpressionable Captain Falcon.    From Wordnik.com.  [The Cruise of a Deathtime]

It would be far stranger were it to fail of effect even on so unimpressionable a thing as a six-story red-brick tenement house.    From Wordnik.com.  [White Ashes] Reference

She remained for some time apparently unimpressionable, tearless, sighless, but in the innermost depths of her heart moved mighty passions.    From Wordnik.com.  [Clotel; or, The President's Daughter: A Narrative of Slave Life in the United States. By William Wells Brown, A Fugitive Slave, Author of "Three Years in Europe." With a Sketch of the Author's Life] Reference

Those have traduced you who call you unimpressionable.    From Wordnik.com.  [The Burning Spear] Reference

This tranquillity of spirit owed nothing to an unimpressionable mind or.    From Wordnik.com.  [The Mirrors of Downing Street Some Political Reflections by a Gentleman with a Duster] Reference

Besides though her voice struck emotion, she herself was unimpressionable.    From Wordnik.com.  [Sandra Belloni — Complete] Reference

There were a dozen women she might have had with her, unimpressionable women.    From Wordnik.com.  [The Awakening and Selected Short Stories] Reference

Spiritual movements have always found some relatively unimpressionable classes.    From Wordnik.com.  [Some Christian Convictions A Practical Restatement in Terms of Present-Day Thinking] Reference

Again that picture came to him -- unimpressionable as his life had rendered him.    From Wordnik.com.  [The Slave of the Lamp] Reference

Now Duncombe was a young man who prided himself a little on being unimpressionable.    From Wordnik.com.  [A Maker of History] Reference

You are a very impressionable woman; he is a singularly cold, unimpressionable man.    From Wordnik.com.  [The Malefactor] Reference

"Leslie is such a steady, unimpressionable boy, you see," she said, apropos of nothing.    From Wordnik.com.  [The Hollow of Her Hand] Reference

The unimaginative, unimpressionable nature of Godfrey, revolted against the sudden change.    From Wordnik.com.  [Stuart of Dunleath: A Story of Modern Times] Reference

His identification with his unimpressionable neighbour's mood had shown him what to expect.    From Wordnik.com.  [Initials Only] Reference

This made itself perceptible even to the toughened and unimpressionable nerves of Inspector Dunbar.    From Wordnik.com.  [The Yellow Claw] Reference

No, but still it is very unpleasant to live with such unimpressionable, incomprehensible creatures.    From Wordnik.com.  [Agnes Grey] Reference

Her companion, tall, gray and unimpressionable, listened as if through coercion and not for pleasure.    From Wordnik.com.  [Nedra] Reference

Douglas was among those unimpressionable younger men who would not believe the Union to be in danger.    From Wordnik.com.  [Stephen A. Douglas A Study in American Politics] Reference

Even in this middle-aged unimpressionable assembly, his indignant self-control had a certain influence.    From Wordnik.com.  [The Perpetual Curate] Reference

But you can't always entirely tell what will happen, especially if the victim is husky and unimpressionable.    From Wordnik.com.  [At Good Old Siwash] Reference

He threw away his cigar with an impetuosity oddly out of keeping with his somewhat rugged and unimpressionable nature.    From Wordnik.com.  [The Odds And Other Stories] Reference

I will give my own experience the first, which is striking to me, because I am very unimpressionable in these matters.    From Wordnik.com.  [Inquiries into Human Faculty and Its Development] Reference

She is handsome, energetic, executive, but to me she seems unimpressionable and temperamentally incapable of enthusiasm.    From Wordnik.com.  [My Antonia] Reference

Flossie's palpitating heart told her that she was really making an impression on this singularly unimpressionable young man.    From Wordnik.com.  [The Divine Fire] Reference

They could see no reason for keeping up with a girl who, under her jocularity, was cold, self-centered, and unimpressionable.    From Wordnik.com.  [The Song of the Lark] Reference

They 'were soon speculating on the unimpressionable house in its clump of wood midway below, which had no response for anxieties.    From Wordnik.com.  [The Amazing Marriage — Complete] Reference

I was but a boy of twelve when I had seen her last, but she had impressed even my unimpressionable age with a sense of her charm.    From Wordnik.com.  [The Four Pools Mystery] Reference

Even the most stoical, unimpressionable men in the party looked at each other in bewilderment and -- awe, there was no doubt of it.    From Wordnik.com.  [Truxton King A Story of Graustark] Reference

Now a grown man -- that is to say, a comparatively unimpressionable man -- that is again to say, a man past the age when to enjoy the.    From Wordnik.com.  [On The Art of Reading] Reference

Fate is never so unkind as to those who blindly resist her and into the lap of stoic and unimpressionable she pours the horn of plenty.    From Wordnik.com.  [Madcap] Reference

Ah! what mad desires dashing up against some rock of obstruction or indifference, and flung back again from the unimpressionable granite!.    From Wordnik.com.  [The History of Pendennis] Reference

Accustomed for years to rise at all hours, in all weathers, unimpressionable, calm and strong, he seemed superior to the course of events.    From Wordnik.com.  [A Tale of a Lonely Parish] Reference