<p>warblers is correct; if it helps, I'd just like to add some more info:</p>
<p>Myself, like warblers said, is a reflexive pronoun. When the subject and the object of a sentence are the same, then the object must be in the reflexive case:</p>
<p>I gave it to myself.
I hit myself.
You understand yourself.
The dog chases itself.</p>
<p>(Excuse the sentences.)</p>
<p>It can also be used in the emphatic case:</p>
<p>I myself read the book.
I looked over it myself.</p>
<p>A general rule of thumb is that if you don't have an object, or, if you do, and the object is different from the subject, then you shouldn't be using a reflexive pronoun (I'm disregarding the emphatic case).</p>
<p>In this particular case, you are introducing a new clause, as you are using either the conjunction "whereas," or "but." A clause has its own subject and predicate.</p>
<p>Ben and younger version of myself did not (understand the concept).</p>
<p>Ben and you make up and the plural subject, and they should both be in the subjective case: I, you, he/she/it, we, you (pl.), they. This is what happens in warbler's example of "Ben and the younger I did not." However, in your example, you use the preposition "of," which requires the objective case:</p>
<p>of me
of you
of him/her/it
of us
of you (pl.)
of them
(of whomjust for fun.)</p>
<p>So, putting all of this together...</p>
<p>You start with your main clause: "He understood the concept,"
You introduce your subordinate clause with a conjunction, either "whereas," or "but."
You start with your subject, understanding when to use the subjective or objective pronoun: "Ben and the younger version of me," or "Ben and the younger I."
You complete your verb: "did not."</p>
<p>Throughout all of this you realize that you aren't using the objective or emphatic case, and therefore you don't need to use a reflexive pronoun.</p>
<p>So there are a lot of little things that go towards putting this sentence together. It's not exactly a simple grammar question if you disregard your ear and actually try and figure it all out :)</p>
<p>If I got anything wrong, please correct me.</p>