33 for Kirk jives with my math (he says he's 34 in The Deadly Years which aired the following season). Just based on what I know about kids and their memories, Riley can't be more than 8 or 9 years younger than Kirk and is more likely closer in age. Dr. Leighton seemed quite a bit older....
I'm with Zardoz, this pretty much writes itself and it would be a shame if they dodged the chance to explore how such a negative experience could have motivated Kirk in his career.
Thanks to Ron Salon for the signature banner!