adjectives - Word that describes people who are easily impressed?

Consider susceptible ("likely to be affected by something", "easily influenced or tricked; credulous" and "(medicine) especially sensitive, especially to a stimulus"); and also consider impressionable ("Susceptible of impression; capable of receiving impressions; emotional"). An "impressionable person" may be someone on whom it's easy to make an impression, or may be someone at a formative stage such that impressions will last. Note, making an impression on someone can differ from impressing them.

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