Its always a great pleasure to share my passion for mathematics and physics with like-minded people. Sometimes a small group of enthusiasts get together and request specific subjects such as aspects of astrophysics: Dark Matter & Dark Energy, Black Holes, Inflation etc. This collaborative approach enables them to share ideas, materials and resources as a team.
For the more ambitious students it is possible to take A Levels part time at a local technical college. Universities such as Royal Holloway (University of London) give talks and lectures on how mature students can access higher education, sometimes without A Level qualifications, and offer possible funding options.
Details of their mature student programme "Access to Education", can be found on the link below:
https://www.royalholloway.ac.uk/student-life/being-a-student/mature-students/
For discussion groups, I would recommend an initial face-to-face gathering at my home office, for participants to get to know each other and discuss particular areas of interest prior to commencing in-depth study.