Great bike for starting out in triathlon. Still a very fast bike with a number of upgrades. Shifts and brakes great. From measurements it's a size L. Should fit someone in the 5"10 height range. 
 
Drivetrain
Component Group: Shimano 105
Bottom Bracket: Shimano FC-5502 175mm
Chain: Unknown
Cassette: 10-speed, 11 - 25 teeth
Crankset: Shimano 105, 39/53 teeth (?) - Shimano FC-5502 175mm
Shift Levers: Shimano 105 STI Dual Control ??
Pedals: Keo2 
 
Wheels 
Hubs: Shimano R-540 (Front), Shimano R-500 (Rear)
Rims: Shimano WH-R540, 16-hole (Front), Shimano R-500 (Rear)
Tires: 700 x 23c Continental Grand Prix 23mm 4 Season 
Spoke Brand: Shimano stainless steel, bladed (Front)
Spoke Nipples: Aluminum nipples
 
Cockpit
Extensions: Vision
Handlebar: Vision
Handlebar Stem: Cinelli ANT
Saddle: Ready to Race
Seatpost: Giant SL Composite Aero, 27.2mm diameter (?)
 
Brakes
Brakeset: Tektro RX 4.1
 
Accessories
Pedals:  Look Keo2Max Carbon
Pump: Included
 
Frameset
BB Shell Width: 68mm English
Frame Construction: TIG-welded
Fork Brand & Model: Giant Composite Aero
Headset: Ritchie Pro
Fork Material: Carbon fiber composite w/aluminum steerer, aero crown
Frame Tubing Material: Aluxx SL aluminum