how can you know Franklin was born on 2003? lol
he could easily have 15 years on X2 and one they do the crossover, he could easily have 30 years.
X2 was 10 years ago, if the crossover happen in... lets say... 2018, he would have 28, in that case.
if he had 20 years on X2, he would have 35.
everything is possible