Sola Fide dilemma: When did Abraham turn 100 years old?

I've come upon another argument that I believe further turns up the heat on Protestants claiming Romans 4 as their own. Though many don't realize it, Protestants basically 'tune out' after verse 8 in Romans 4, treating the rest of the chapter as an appendage. I've already written extensively about the horrendous exegesis Protestants have for Romans 4:1-8, so I wont go into that now. Instead, I'm going to focus on Romans 4:16-22,

16 That is why it depends on faith, in order that the promise may rest on grace and be guaranteed to all his offspring—not only to the adherent of the law but also to the one who shares the faith of Abraham, who is the father of us all, 17 as it is written, “I have made you the father of many nations [Genesis 17:5]”—in the presence of the God in whom he believed, who gives life to the dead and calls into existence the things that do not exist. 18 In hope he believed against hope, that he should become the father of many nations, as he had been told, “So shall your offspring be.” [Gen 15:5] 19 He did not weaken in faith when he considered his own body, which was as good as dead (since he was about a hundred years old), or when he considered the barrenness [Greek: deadness] of Sarah's womb. 20 No unbelief made him waver concerning the promise of God, but he grew strong in his faith as he gave glory to God, 21 fully convinced that God was able to do what he had promised. 22 That is why his faith was “counted to him as righteousness.” [Gen 15:6]

As I've noted elsewhere (here and here), Romans 4:18-22 is crucial for interpreting Romans 4:3, since here is where Paul 'unpacks' Genesis 15:6. The reason why Protestants gloss over 4:18-22 is precisely because it doesn't fit their idea of "faith" being an "empty hand" rather than something pleasing in God's sight. To build on this, I offer two more arguments, one I learned from someone and one I came up with on my own.

The first example I actually learned from an Arminian Protestant (basically the antithesis of Calvinistic Protestants), who pointed out that verse 17 speaks of God (a) giving life to the dead, and (b) calling into existence things that do not exist. Now these two categories could be speaking generically (i.e. of course God can raise the dead), but there seems to be a more direct meaning. Note that Paul is quoting Genesis 17:5 here, where God changed Abraham's name from (originally) Abram to now being "Abraham" - which literally means "father of many nations". Genesis 17:1-10 is about God recalling the covenantal promise and unfolding it (Gen 12-15). Here is where God changes his name. This is by no means insignificant. Yet the irony here is that Abraham at this point (99 years old) was not the father of many nations, in fact he wasn't even a father of Isaac yet! So God is essentially saying he wants people to go around calling this man "Father-of-Many-Nations" despite the fact this reality does not (yet!) exist. This is most likely what Paul means by God calling things one way that do not (yet) exist. And this conforms, likewise, to giving life to the dead, in this case Sarah's "dead" womb!

This plays right into what I noticed, which is that in verse 19 Paul speaks of Abraham being almost 100 years old and the barrenness of Sarah's womb. The question is: when did Abraham turn 100? It could not have been in Genesis 15:6, for Genesis 16:1ff tells us that after a while Abraham got worried and tried to make himself father of many nations by his own power, by sleeping with Hagar, producing his son Ismael (though God refused to consider Ismael the lineage of the Promised Seed, Gen 17:15ff; 21:12). In Genesis 16:16 it tells us that Ismael was born when Abraham was 86 years old. Now this could be said to be 'close' to 100 years old, but that assumption doesn't fly in light of further facts.

Continuing on the Genesis 17 context (Rom. 4:17), notice what the chapter goes onto say:

15 And God said to Abraham, “As for Sarai your wife, you shall not call her name Sarai, but Sarah shall be her name. 16 I will bless her, and moreover, I will give you a son by her. I will bless her, and she shall become nations; kings of peoples shall come from her.” 17 Then Abraham fell on his face and laughed and said to himself, “Shall a child be born to a man who is a hundred years old? Shall Sarah, who is ninety years old, bear a child?” 18 And Abraham said to God, “Oh that Ishmael might live before you!” 19 God said, “No, but Sarah your wife shall bear you a son, and you shall call his name Isaac. I will establish my covenant with him as an everlasting covenant for his offspring after him.

Look what Abraham said: shall a 100 year old man and woman way past childbearing years have a child at this point our their life? So when Paul said these words in Romans 4:19, he really had in mind Genesis 17, not Genesis 15! This is huge, for it means the "faith" that Paul had in mind was a growing and persevering faith (as is obvious by the plain language), and thus this faith was not an 'empty hand' at all. In fact, this texts suggests Abraham grew in righteousness as he continued to grow in trust beyond the odds. The biological facts of life told him one thing - that having a child a that point is biologically impossible - while his faith told him God can do anything.

Thus we have one more nail in the Sola Fide coffin.