My time recording system tells me I started grammar properly in the same week as WaniKani (mid Jan 2021). Likely got motivated by the new kanji and wanted to put it into practice
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I started with Tae Kim’s guide and have been using it ever since. The only thing that caused me some pain so far was 何か, 誰か and the likes, since I got too comfortable with か as a question particle. Also, certain adjective conjugation forms like 暖かかった, since my echoic memory gets the better of me sometimes
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I don’t have any special tricks, but if I feel I’m weaker in some area, like adjective conjugation, I simply conjugate all of the adjectives from my word list on paper, reading each conjugation pattern aloud to memorize the sounds. Same before with verbs.
Never too early to get into it! Well, OK, if you don’t know kana it is probably too early… (but you don’t have that problem because you are here)