Most particularly one person I was talking to was in her thirties, but I got a similar 'drop formality after the introductions' from someone around 19 in another particular case I remember, so, yes, definitely 'young people' in their language use. 50+ that I've corresponded with never drop the plain form for even a moment, it's true.
And I don't mean to say only in offices - I believe I mentioned 'with strangers' ... and perhaps that sounded dismissive, but I do understand whenever you first meet someone you speak formally, and everyone working in a shop is facing the public - who are both strangers -and- customers - and so speaking formally all day. Every person on the street who isn't a friend or a relative is a stranger.
Of course you need it. I'm not saying you -don't- need it.
However, as someone who's not in Japan... I can read all day or watch dramas all day, and only encounter the polite forms when a character visits a shop. Of course, the broadcast news and really any non-fiction broadcast requires the polite form all the time too, so I suppose it depends on your interests here, but enjoying -any- sort of Japanese fiction in any format is flatly impossible without a good command of the plain forms.
My classes taught polite form almost to the exclusion of plain form - we used plain form in embedded sentences, of course, and the textbook included a little plain form of families speaking among themselves, but, on the whole it was neglected - never used in in-class exercises or instructor-authored exercises. Between the de-emphasis of the plain form and the lack of kanji coverage, ... well, my formal study gave me a little head-start on my self-study (it would have been a larger jump-start if I hadn't practically stopped studying Japanese for two years right after graduating college... :O)
Anyway, my dissatisfaction with that curriculum may color my perspective, but I really do believe that it's simply logical to introduce things from the simple to the complex (and yes, discourage your students from trying to start conversations with real Japanese before the polite forms are introduced.)
But still, even if you think the polite form -should- be taught almost to the exclusion of the plain form, and that students need to learn it early before they cause offense... it's certainly possible to introduce dictionary form in week 1, past form in week 2, continuative form in week 3, and masu form in week 4. That's not even a challenging schedule ... well, depending on the level of particle, kanji, and vocabulary study in the mix. I should think that learning the polite forms before the first month is out would satisfy anyone that it's being introduced 'soon enough' without teaching the grammar backwards.
And I don't mean to say only in offices - I believe I mentioned 'with strangers' ... and perhaps that sounded dismissive, but I do understand whenever you first meet someone you speak formally, and everyone working in a shop is facing the public - who are both strangers -and- customers - and so speaking formally all day. Every person on the street who isn't a friend or a relative is a stranger.
Of course you need it. I'm not saying you -don't- need it.
However, as someone who's not in Japan... I can read all day or watch dramas all day, and only encounter the polite forms when a character visits a shop. Of course, the broadcast news and really any non-fiction broadcast requires the polite form all the time too, so I suppose it depends on your interests here, but enjoying -any- sort of Japanese fiction in any format is flatly impossible without a good command of the plain forms.
My classes taught polite form almost to the exclusion of plain form - we used plain form in embedded sentences, of course, and the textbook included a little plain form of families speaking among themselves, but, on the whole it was neglected - never used in in-class exercises or instructor-authored exercises. Between the de-emphasis of the plain form and the lack of kanji coverage, ... well, my formal study gave me a little head-start on my self-study (it would have been a larger jump-start if I hadn't practically stopped studying Japanese for two years right after graduating college... :O)
Anyway, my dissatisfaction with that curriculum may color my perspective, but I really do believe that it's simply logical to introduce things from the simple to the complex (and yes, discourage your students from trying to start conversations with real Japanese before the polite forms are introduced.)
But still, even if you think the polite form -should- be taught almost to the exclusion of the plain form, and that students need to learn it early before they cause offense... it's certainly possible to introduce dictionary form in week 1, past form in week 2, continuative form in week 3, and masu form in week 4. That's not even a challenging schedule ... well, depending on the level of particle, kanji, and vocabulary study in the mix. I should think that learning the polite forms before the first month is out would satisfy anyone that it's being introduced 'soon enough' without teaching the grammar backwards.

