I'm in a golf club, and here is my attempt at explaining the situation from my limited understanding of the complex membership rules:-
Clubs will usually have full membership and 5 day membership for adults. 5 day members cannot normally play at weekends, but there will be a few weekend competitions organised over the year that they can play in. Obviously 5 day membership is cheaper, and usually new members join under this category, progressing to full membership after a period of time.
Associate members is a closed category - it used to be the only available category for women in many clubs. When clubs opened up full membership to women it was considered unfair to force ladies who had been long-standing members of a club to have to pay full membership, so for women who didn't want to take up full membership (and having to pay the entrance fee involved), they were left as lady associates.
Junior members are usually taken on from about age 12 - 13 at a lot less than the full annual membership fee. They will usually be offered specialised group lessons during holiday times at little (or even no) cost. Their playing times on the course will be quite restricted and there will be a limited number of competitions open to them.
It is understood that when Juniors reach 18 they are rarely going to be in a position to pay for full membership fees - and often an expensive entrance fee - but the club doesn't want to lose them as a member. So the intermediate (student) category is the mechanism to deal with this. The fee is increased slightly but the playing rights increase hugely, in many clubs to practically the same level as a full member.
After the intermediate member has finished their further education it is expected they would apply for 5 day or full membership, and clubs would normally set a cap on the latest age (in the OPs case it's obviously 23) intermediate membership can be held until.
All that said, golf is an expensive sport, and if the OP isn't sure it's for life, then it might be worth taking a cheap membership in one of the many clubs outside city areas, and then playing in the local club on a green fee basis.