Why is Harry so Tall?

[ElJefe81]

Intent: She was targeting his birthtime exactly by using a mix of slower-time and faster-time locations. Thomas was the dry run, hence his birthday on exactly Valentine's. By changing her subjective timeline relative to objective time, she could ensure Harry's birth at the optimum time to produce a starborn. Side effect: He's tall.

I like this.  Also because it would indicate his mother's mastery of The Ways wasn't limited to just physical utility but also temporal.

[Icecream]

The trend over the last 100 or so years seems to be that children are growing taller than their parents due to better nutrition. Ebeneezar may have stunted growth from his youth due to poor nutrition or food availability.  There are alo other relatives Harry may have gotten the height gene from, his father and his grandmothers side.

Main reason is because Jim picked that as a particular characteristic. 

[Conspiracy Theorist]

It seems awfully coincidental that they both have birthdays on significant dates, and we have only dealt with the consequences of the temporal issues of the NeverNever as regards Rashid’s aging and Murphy’s absence in Proven Guilty, but we have been reminded since the NeverNever was introduced.

She was in the control of Lord Raith for Thomas, so this is suggesting he was trying to breed a Starborn with Wizards powers and a hunger demon. Given the reproductive issues Whampires have, conception could not be guaranteed for a particular time so Margaret with her knowledge of the ways would have been the only option (other than Rashid, ruled out for other reasons)

[The_Sibelis]

Elaine was born on the summer solstice in opposition of Harry too.. she's also rather tall. Perhaps it's part of the starborn thing? Stature equals actual stature lol.

[Feral Plum]

I still want to know who his grandmother, Ebenezer's wife, was. I feel we have seen her or - if she is dead - heard of her. Anastasia would have known her. She was in America.
I suspect Mac of involvement.

[Mira]

She was in the control of Lord Raith for Thomas, so this is suggesting he was trying to breed a Starborn with Wizards powers and a hunger demon. Given the reproductive issues Whampires have, conception could not be guaranteed for a particular time so Margaret with her knowledge of the ways would have been the only option (other than Rashid, ruled out for other reasons)

Just found it in Battle Ground, Eb was only five foot six!

Except she wasn't, she didn't consider it until she met Malcolm. Lash confirms that Margaret left Lord Raith for a reason, it was so she could have a star child with Malcolm.