[@Crusader Lord]
Glad to see you stopped by again. I'll answer your question(s) as best I can.

The term for a child born from an angel and a demon/devil's union is called a 'Nephilim'. At least if the parents are of those races. In your case however, the original progenitors were both halfsies, meaning their offsprings would be quarter-nephilim. Subsequent generations would become more watered down.

Now, to answer the major quesation. In my personal preference, I have never liked the idea that half-breeds gain benefits from both parents and, usually, none of the drawbacks. I also am not particularly fond of the "the blood lay dormant for X time until SUDDENLY awakening!"-trope, especially when said 'suddenly awoken' powers present themselves in a fantastic or incredibly impressive way.

To put it simply; I'm fine with whatever age you want your character to be, and if you want to make them a 1/32nd-part Nephilim, that's totally fine. But don't expect to be given special powers or abilities, because the more watered down the lineage is, the less remarkable and less power it holds in comparison to the original. You'll be able to have traits of both angels and devils/demons, for sure, but compared to something like an Aasimar (celestial-blooded human) or Tiefling (fiend-blooded human), or even a 1/4 or 1/8th Nephilim, your character's "racial bonuses" would be fairly minor, in all fairness.

Additionally, I'm sorry to say, but I will [b]not[/b] be making the Main Protagonist in such a way as to facilitate or make another character 'work'.  This is due in part to the fact that I already have a set idea and concept for them, and due in part to if I do it for one person, I should do it for everyone - and that could get real messy, reeeaaaal fast. o_O;

I hope that answered your questions. :o