Certainly if you don't have maths and/or English language GCSE then that can close the door to many possible job opportunities. You should be able to find a college or adult learning centre where you can take them with part-time study in September this year, it is government funded and should be free to you. If you wanted to start sooner then free functional skills classes might also be available now.
Whether doing A levels at a later age is beneficial depends on what you hope to do. If university is your goal then many people would chose an Access Course over trying to do A levels.