2015 - 1983 = 32 years
Why is it so unrealistic that Han & Leia and Luke & mystery woman (I won't say Mara Jade anymore since she could be negated by the ST) waited 5-7 years after the events of Return of the Jedi to have kids? If they did, the first born would be 27 years old at the start of the movie and would still very much be considered a 20-something. 20-something doesn't have to mean 20 or 21.
Leia would be having her first kid at 40 then (and Han 54). Sure medical science was better in the Star Wars universe, but you must admit having kids that late isn't typical. Especially for women.
Maybe Leia just froze some embryos in carbonite so she could focus on her career...
I think of it this way... Luke Skywalker is a hero - like Lincoln. Did amazing things. Made history. Saved humanity.
Nobody gives one damn about Lincoln's kids.