I know tons of Ryans ranging in age from 5 to 30. That being said, if you really love the name that much I don't think it should get in the way of your using it.
Ryann on a girl is nms but it's not terrible; I think
Ryann Skye is prettier than
Ryann Storm. One thing: I don't pronounce it the same that I pronounce
Ryan. I say it as ry-ANN with the emphasis on the second syllable. Just an FYI in case you were planning on having people pronounce it the same as
Ryan; they might not do so automatically.