Timeline question: How old was Aegon when Volantis was defeated during the bleeding years? It seems confusing since Argilic was said to have slain the king of the reach twenty years after it, Aegon would seem to have been only a boy at the time, since he was born less than three decades before he began his conquest of westeros, how do you make sense of this, could he really have participated at such an age or is this a case of the dates being wrong?

Good question! As one might expect, Volantis’ rise and fall in the Century of Blood was a somewhat drawn-out process. So here’s my best guess of how the timeline works out:

• We know that the Doom of Valyria provoked “immediate political upheaval,” with revolutions in Tyosh, Lys (and presumably Myr) against the dragonlords. (This is a bit confusing since WOIAF tells us the Free Cities had bought their right to self-government from Valyria, but it’s possible that this right was somewhat honored in the breach, especially in a crisis, or that the Free Cities acted out of fear that their rights would be taken by the dragonlords in said crisis.) 
• We also know that the Volantenes “quickly laid claim to Valyria’s mantle,” which suggests that the war began pretty quickly after the Doom, so probably within a year or two of 114 BC.
• We also know how long the ascendancy of Volantis lasted: “a Volantene fleet took Lys and a Volantene army captured Myr, and for two generations all three cities were ruled from within the Black Walls.” (ADWD) Given that a generation is roughly 30-35 years, that suggests that the Volantenes were successful in their expansionist offensive from around 114 to around 53-44 BC. 
• Then we learn of a whole bunch of stuff happening in quick succession: Volantis tries to conquer Tyrosh, Pentos joins the war on Tyrosh’s side, Lys and Myr rebel, Braavos finances Lysene resistance, and the Storm King defeats Volantene attempt to retake Myr. This lets us know roughly when Argilac was warring in the Disputed Lands – given his age (Argilac was born roughly 60 BC), and the fact that this campaign is the first campaign after his boyhood that’s mentioned in the text), but also comes after all of the previous events, it probably happened closer to 44 BC. This would place the Battle of Summerfield around 22 BC. 
• We then get a bunch of details that give us some hints as to when Aegon was involved. We learn for example that Aegon was “still-young,” that his intervention came “near the end” of the Century of the Blood, and that he joined the war at the behest of Pentos and Tyrosh (which places it definitely after their alliance). Now Aegon was definitely born in 27 BC, which means that he really couldn’t have partaken much before 13 BC – but this is only problematic if we get overly finicky about the “Century” part of the “Century of Blood.” 
• So Aegon gets involved very late in the war, burns “a Volantene fleet that was preparing to invade” Lys in what must have been a very last-ditch counter-offensive, and then Dagger Lake and the Dothraki show up and the elephants overthrow the tigers – which we know happened right around 0 AC, since Aegon VI describes the elephants as having “ruled the city for three hundred years” in the year 300 AC. This suggests that Aegon’s intervention must have happened only a few years before the Conquest, at most around 4 BC, when he was in his early 20s. (Which counts as still-young, I suppose.)
• Moreover, we also learn that “shortly after his role in defeating Volantis it is written he lost all interest in the affairs of the east…’[and] turned his gaze west,” which are the last words in WOIAF before the account of the Conquest begins. This is further evidence that Aegon’s involvement must have happened only a few years before the Conquest.

As long as we’re willing to accept that the Century is more of a handy moniker than a precise chronological metric, the problem resolves itself nicely.