Reading a notice with a hidden condition

The 'free' part is correct: 参加費：無料 means there is no participation fee. The 'anyone can just turn up on the day' part is wrong on two counts. First, 申し込み (application) is required by 3月5日（水）by phone or email, so you cannot simply arrive. Second, 定員：先着30名 with ただし、定員に達し次第締め切ります means places are first-come-first-served up to 30 and close as soon as the limit is reached, so even applying by the deadline does not guarantee a place. A good answer separates the accurate claim from the inaccurate ones and cites the exact wording that supports each judgement, rather than accepting or rejecting the whole statement.

The 対象 line says 中学生以上, 'junior high school students and above'. A Year 7 student in Australia is usually in the first year of secondary school, which corresponds to 中学1年, so he meets the minimum age. The judgement depends on mapping the Australian year level to the Japanese school category rather than reading 中学生 as 'middle school' in the Australian sense. Two other conditions: you must bring 筆記用具 (writing materials) and your own drink, since only writing materials are listed under 持ち物 and drinks are explicitly your responsibility (飲み物は各自ご用意ください). Also, there is no parking (駐車場はありません), so you must come by public transport. Any two of these are acceptable, provided each is tied to the notice text.