noajthan, thank you for all your help.
You need to itemise your timeline and activity/ies in UK together with any (possible) dependency on your sponsor (if any) and your age at each major stage - either here or on back of the proverbial beer mat.
Ok, I have done that below. To be honest, now that I look at my situation, I highly doubt that much can be done for the time being, but maybe there is something I'm missing etc.
To make the question of age clearer: I was born in December 1991.
July – September 2010: I joined my mum in the UK and remained dependent, living at home.
September 2010 – June 2011: I attended an ESOL course full-time; I was still dependent on my mum and not working.
June – September 2011: I was dependent on my mum, living at home before starting university. I had a weekend job, but it wasn’t official, no contract etc.
September 2011 – May 2012: I was a full-time university student, still dependent on my parent.
May 2012 - July 2013: I started work before my 21st birthday. I mostly worked full-time, however for a few weeks during the semesters when I was really busy in uni, I would do 3-4 days weekly.
July – August 2013: I took a holiday before starting another job, had my job offer already and the job was sorted via university.
August 2013 – January 2014: I worked in Dublin – less than 6 months in total, it was in the frame of a compulsory industrial placement for the university, I have an official confirmation from the university for it. I worked full-time.
January – June 2014: I worked the other part of my placement in the UK, full-time.
June – September 2014: My placement contract ended and the employer didn’t keep me on as they were “overstaffed”. I made a big mistake here and listened to bad advice – I didn’t register with Jobcentre Plus. I didn’t know you could register without taking benefits, and I didn’t want to take any benefits from the government, to make sure I was a person of “good character” (I know…). I kept looking for work actively though, I have a whole folder with e-mails printed off, application forms etc. for a variety of jobs. During this time I was living off my savings, my mum helped me out a bit but there would be no official trace of it (cash in hand), I was living with my boyfriend at the time as well, so not in the family home.
September 2014: I finally got a job – however, I only kept it for 3 weeks as the atmosphere was really bad and I was harassed by a senior colleague (I know it sounds rather dodgy but there is a trace of this employment on my record so I have to mention it. I wrote a letter of complaint to the regional manager of this company as this incident was really bad, but I didn’t take them to court or anything of that sort – I’m not even sure if that’d be counted as involuntarily unemployed…).
October – 26th November 2014: I was looking for work again, I have applications and letters as well (but still not registered with Jobcentre Plus).
26th November 2014 – June 2016: I got a job and was in the last year of university. It was a zero hour contract (hotel), but I worked full-time most weeks. I kept the job after the graduation from university in July 2015. This industry is rather tricky, because most contracts are zero hours and the amount of working hours depends on the needs of the business. It was mostly full-time in my case though. In the meantime, I moved back in with my family (this time paying rent etc.), but I suppose that doesn't really matter.
June 2016 – now: I have a steady, full-time job and a contract with guaranteed hours.
I suppose that my absolute best chances of getting any document is to start counting my "eligible" time from November 2014, and so, apply in December 2019 (if I still can as per the new UK rules, that is - hopefully so). I wish I had found this forum and was smarter about my moves way earlier on, I could have avoided many stupid mistakes - but well.
Added:
Interestingly, I consulted an immigration lawyer (only as an initial consultation, because for anything more I have to pay £500, of course) and I have just received his answer (in my e-mail I presented my situation in detail like above) - he states that, "because I remained in full-time education from July 2010 until July 2015, that in itself makes me dependent on my mother and thus eligible to apply". He goes on to explain that this is because my mother paid for my ESOL course in the first year and then during university I received all of my student finance based on my mother's employment and financial circumstances (and not mine).
Strange - but then again, as lawyers go, he might be wanting me to pay and then it might turn out that I'm actually not eligible...