Actually, since "Heaven" exists in a seperate dimension and the goddesses use energy from the Yggdrasil system to maintain thier apperance and clothing in Keichii's dimension, i'd imagine Belldandy could appear as young or old as she wants. During a Yggdrasil system error in the manga Urd regresses to a (very cute) little girl and skuld becomes an adult, though they keep thier "current" personas.
Regardless, Belldandy, Keiichi and the others are as ageless as Tom Sawyer or Romeo and Juliet, forever young- University students and childish pranksters -I'll always see them that way.
11-Jun-2004