And you are misrepresenting, too.
I appreciate now that you are saying it wasn't your intent, but your original comment seemed a bit shaming, as though 'whinging' was down to parental fault and a 'good' parent who 'managed' behaviour wouldn't have a 21 month old who whinged. It also looked as though you were saying that if you respond to a child 'whinging' at 21 months old, you will have a 'whinger' at 12. 30+ years of developmental and behavioural psychology suggests the opposite.
In all honesty, in 20 years of working with young children I'd say the 21 month old who doesn't 'whinge' is a rare child indeed. Sometimes, in fact, a child you worry about being less vocal and more passive than you would like a 21 month old to be.
You also mentioned nothing about 'managing' this behaviour positively or gently in your post and you still haven't given an indication of how a parent would manage a 21 month old in such a way that what THEY do would be directly responsible, aside from a child's temperament and developmental progress, for ensuring that a 21 month old NEVER whinges.
I know of only two likely scenarios where this can happen: where a child's every need is anticipated and responded to before they can protest about it, or where a child's needs are never responded to if they demonstrate any distress in their response, so they lose the sense that sharing distress with a caregiver has a reinforcing function.
Neither is really optimal, to be honest. 'Whinging' is just communicating with some low level distress because something confuses you - usually in your 21 month old egotistical state that you can't have something you want. There are positive and gentle ways to manage the emotions that arise when this occurs and to support a child in developing communication skills and understanding of the world to reduce incessant whinging, but to expect that at 21 months, an adult can 'manage' this behaviour so that it never occurs is a bit OTT.
In any case, it seriously annoys me when the reason given for managing very young children's distress is because it might annoy other people. No, the reason to manage it is because it's important for a young child to learn to communicate and regulate their emotions for their long term well-being.