Ok. I think I've got something here.

Name: Calvin Lennard
Alias: G-Man
Experience: 50 days
Hometown: Gotham
Age: 18

Powers: Gravity manipulation of self and anything he touches.

Weaknesses: Anything that would hurt a normal person.

Reason for joining Robin: To be part of something bigger and make a difference.

Appearance: Calvin clocks in at 5'9" tall with a build on the lighter side of average. He has medium-length dark brown hair and blue eyes. He is tan enough to have a bit of color to him, but is still pretty light-skinned. Calvin tends to dress plainly in simple jeans and a t-shirt with sneakers.

His 'superhero outfit' is a simple black t-shirt with a white double-sided arrow pointing up and down. This is accompanied by a pair of jeans and sneakers as well as a pair of aviator goggles. Just because aviator goggles are cool. Also identity concealment. 

Brief Bio: Calvin was a high school track and field star who performed incredibly well. Perhaps a bit too well in fact. He dominated pole vaulting, shotput, and jumping events with uncanny ease. After winning the regional championship, Matt confronted Calvin and told him that he knew he was using his metahuman abilities to cheat. Calvin fell for the bluff and begged him not to tell. Matt told Calvin that he would keep his secret if he agreed to join him and use his abilities for something a little more worthwhile than simple sporting events. Calvin agreed and joined the Titans.