Is it possible to start a new career at age 30?

I’m gonna be hitting 30 soon, and I am not sure if it’s possible for me to start a new career, something that will lead to a good income to support a family down the line. I currently work two jobs, one during the day, the other at night, I manage to get two sleeps in during the day to make this work. Job 1 is a full time, salaried at £30k. Job 2 is warehouse work 0 hours, but work is readily available and I can choose when to go in. I realised that I can’t do this long term and with all our kids in school soon, I will some time that I can use to help me kick start a new career, I just don’t know where to begin. I have GCSE’s and some mediocre A-levels, but these were attained like 13 years ago and I doubt they will help right now. Has anyone here managed to turn their life in a new direction, successfully late on?