How do I draw age from DOB for use in later questions?

I am conducting a survey on when and for how long people were engaged in sport.
I have a DOB question currently as a text entry in the beginning of the survey.
Several questions later I ask people what year they are involved in a sport category (ie ball sport) as a multiple choice - Multiple select box. The following question asks them to select a year/s they were involved in that sport category (Also a multiple select box).

First question - How can I limit the answers in this multiple select box to the period from a persons DOB to the current date. (As it stands I have options for all years 1920 - 2020 which is a little bit cumbersome).

Following on from selecting the years they were involved in a sports category, I ask them to clarify their exact sport, and the year they were engaged in that particular sport as a Side by Side question where the Columns are various sports, and the Rows are years (Dragged forth as selected statements from the 'years' multiple select box).

Second Question - Is it possible to have the years in the rows displayed as a persons age in years? This goes also for the first multiple select 'years' box.