I just meant number of years training. I avoided going in to more variables. It's also possible if OP is doing 5x double-days per week he'll have more mat time than his friend who is doing 2x single-days.
If we assume 3 years for Karate black belt, then another year for TKD black belt (many TKD places will start you close to black belt if you have one in Karate or TSD), then his friend has 4 years experience, and will probably have 6 years experience by the time of the fight, compared to the friend's 2 years.
There's a lot of factors that can overcome that, including natural talent, study habits, quality of the schools, times per week, size, athleticism, etc. But just in terms of experience, the opponent has a head start, and will probably continue to climb it.