It's for family membership. Not sure v8mini is quite right. If it's just you and you're a junior don't worry, just put your own name in the first junior box and add your DoB, complete rest of form and send with cheque or postal order for £14 to Clacksfield House. Even though you are a junior and pay a reduced membership fee, you're still a full member...

Also you might want to consider asking this sort of question on the BMFA or RCMF forums (or similar UK sites).