Getting an accurate age of comic book characters is an almost impossible task. Marvel established in Powers of X that the X-Men were founded about 10 years ago. So if 1963 was 10 years ago, Jubilee could easily have been around for the height of 80s fashion and still somehow be a teenager. However, given that she adopted a child and nobody thought she was too young, she's likely in her early to mid 20s.
As for their ages with respect to each other. Kitty was 13 in her first appearance in 1980. I'm not sure about Jubilee, but I think she was either 12 or 13 for her debut in 1989. Jubilee should therefore always be younger than Kitty.