That is the very definition of detachment.
Feelings are the core part of you, and not separate from you. Allowing "yourself" to not be defined by feelings essentially means detaching "yourself" from "your" feelings.
> Detachment [...] NOT in the sense of not feeling.
Of course if one is not feeling a feeling in the first place there is nothing to detach from.
> This is natural, effortless and is part of growing up as a human.
So whenever you begin to feel one or more of the following feelings[1] is it "natural, effortless" to experience your peace?
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[1] sadness, loneliness, melancholy, grief, masochism and so on through all the variations such as agony; angst; anguish; anxiety; apprehension; bereavement; bleakness; crestfallen; deflated; dejected; depression; desolation; despondency; disappointment; disconcerted; disconsolate; discontented; discouraged; disenchanted; disillusioned; displeased; disquiet; dissatisfied; distress; dismay; downhearted; dreariness; edginess; fear; fed-up; flustered; foreboding; fretfulness; frustrated; gloominess; glum; grief; heartache; horror; lament; melancholic; miserable; misery; morose; mourning; nervousness; panic; perturbed; regret; sad; sadness; sorrow; sorrowfulness; suffering; tenseness; terror; thwarted; torment; trepidation; troubled; uneasiness; upset; woe; worry; wretchedness