I adore this name! It's my grandfather's name and I would love to use it has a middle name for my future son.
He goes by
Ted which I don't really care for.
Teddy would be cute for a young child and
Theo would be great for a young adult or a middle aged adult. You could also use
Teo I guess.
Teo is a nickname I use for my son whose name is
Matteo and I'm sure it could go just as well with
Theodore.