Kajukenbo, First step is always the hardest?

If you have been reading my other questions related to KJKB you would have noticed that I really do want to join a KJKB dojo and rip myself apart with the training BUT I have one issue standing in my way! The last time I trained in any sports was 4 YEARS AGO, I am about 5"8" and I weigh 70KK, so basically I am a thin guy who is not JUST THIN but has zero strength,zero durability,zero dexterity and etc... some of my close relatives such as my Father advised me to get in shape first before I join the Dojo or even before I think about joining it! He wants me to train in weight lifting for a while and get myself an "athletic body appearance" before joining the KJKB.

I used to practice Judo for 2 years (before the 4 years of training in Nothingness) and I know how painful or atleast exhausting it can be to be lifted and then thrown on the mat over and over again and I expect KJKB to a hundred times worse and I am afraid this might affect my studies as I am a university student (18 years old) with this current "physical appearance". I really dont know, should I join KJKB and cross my fingers? Or should I spend a 6m-1yr-2rs in a gym before I join KJKB?!

Thanks alot!