No, the phrase will ever be does not include the past, but the statement your friend has made is perfectly correct and grammatical.
To explain:
Right now you are the oldest you have ever been.
This is true, unless you are a time-traveller, or your aging process goes backwards. I believe neither of that is true, therefore the statement is true.
Right now you are the youngest you will ever be.
This is also true, because you will never be any younger anytime in the future than you are right now at this very moment.
Imagine a timeline starting at right now, ending in the infinite future. There is no past on this imaginary timeline. At which point, on this timeline, are you the youngest (you will ever be)? At its beginning = right now!
EDIT: Seeing from the comments below your confusion, I'll try to explain this problem a little bit further.
Imagine the following sentence:
Will you finish this project?
This sentence may be expanded to:
Will you, in the future, finish this project?
Since will is a future tense and the future is already implied in it, there's no need for the expanded sentence.
As you mentioned, ever means "at any point in time," which is correct, but let's add it to our sentence:
Will you ever finish this project?
And let's expand our sentence again:
Will you ever, in the future, finish this project?
So, as you can see, ever still means at any point in time, but time is limited by the tense used in the sentence. Therefore, contrary to what you may or may not believe, will ever be does not include the past.
This isn't a question of right vs. wrong. Rather, you are describing style differences. The sentence "I'm not sure this is right" is elliptical, meaning it leaves out words that have a grammatical function in the sentence but are implied.
The word "that" is often omitted.
In regards to your use of "if." This word is informally used to indicate options. The more formal word to use here is "whether," as in "I'm not sure whether this is right." However, that sentence, too, is elliptical. The full sentence, with the implied words in place, is "I'm not sure whether or not this is right."
Leaving out the implied words is not incorrect. As I said, it's a style choice. If a sentence is clear without the implied words, and if the sentence has an appropriate level of formality according to the purpose and audience, leaving out the implied words is generally acceptable.
Best Answer
The rule you have been told has some validity, but is too general.
English speakers don't use a will with simple future meaning after if:
not
But will can also convey intention or willingness, so with an animate subject (especially second person) will can work
meaning something like if you are willing to come.
So
is normal, as is
But while
doesn't make sense,
can make sense, with the special meaning of if you are willing to jump - it's an invitation, or a dare.