In Harry Potter, is it only children who can do 'instinctive magic'?

Question

Before coming to Hogwarts, many child witches and wizards display some sort of latent magical ability, by performing magic instinctively: e.g. Harry making his hair grow incredibly fast or making a pane of glass disappear, Neville bouncing when dropped from a window, etc. Such acts appear to be motivated only by the subconscious: Harry didn't want to have almost no hair, but didn't know he could do anything about it.

Does this sort of 'instinctive' magic manifest only in children?

Of course, adult witches and wizards have had training and so they're likely to know what kind of spell to use and be able to do so consciously. But say they can't: if an adult is in some life-threatening situation and doesn't know how to escape, is it possible for them to cast some instinctive non-verbal spell that they don't even understand in order to save themselves, as children can do so easily?

Answer 1

Another example worth noting is that of Ariana Dumbledore. Although she was still young (fourteen) when she died, her magic was described as completely uncontrollable with no sign of improving, so presumably this would have carried on into adulthood. Her lack of control was due to emotional scarring in her childhood. Ariana was obviously a lot more vulnerable to her emotions than a typical fourteen year old.

Based on this, I would make an educated guess that the instinctive magic doesn't happen based on age, really, but on the level of emotional vulnerability, fear, or trauma that the wizard or witch is experiencing. As a typical witch gets older, they may still experience fear, such as in a battle situation (as we see often in the books) but their training overcomes their instinct, because magic with a wand is a lot more useful and reliable - unless, like Ariana, they have not had training or are still vulnerable.

As a side-note, and pure speculation, it also seems like the more you know the "proper" way to do something, the less likely you are to instinctively protect yourself from it. For example, when Neville was dropped out of a window, he would panic, and have no genuine idea how to protect himself from the fall, so instinctive magic took over and he bounced. However, in other situations where characters are falling, this isn't the case - there's a scene in the books (although I can't remember which one) where Hermione has to cast a cushioning charm to prevent them all from smashing into the ground. She knew what she had to do and that she had to do it quickly, so she'd be focusing on getting that done rather than letting her instincts ("aAAAAAAAhhhhh") take over.

Answer 2

If you take this statement from Rowling at face value then anyone at any age would be able to use instinctive magic:

You can do unfocused and uncontrolled magic without a wand (for instance when Harry blows up Aunt Marge) but to do really good spells, yes, you need a wand.

from 2001 interview

Additionally:

I'd speculate that Lily's sacrifice for Harry may also be considered instinctive magic, as she was wandless, yet still used magic To save Harry's life.

Answer 3

Adults likely can do instinctive magic, though it’s less common.

Harry and Mr. Weasley discuss instinctive magic when Harry’s trying to figure out how he cast a spell at the Dark Lord. Mr. Weasley says that often, being in a pressured situation causes wizards to do magic they never dreamed of, and he doesn’t say only children can. In addition, he thinks this is what happened to Harry, despite Harry being just days away from being of age.

“No,’ said Harry. ‘The bike was falling, I couldn’t have told you where Voldemort was, but my wand spun in my hand and found him and shot a spell at him, and it wasn’t even a spell I recognised. I’ve never made gold flames appear before.’

‘Often,’ said Mr Weasley, ‘when you’re in a pressured situation you can produce magic you never dreamed of. Small children often find, before they’re trained –”
_{^{- Harry Potter and the Deathly Hallows, Chapter 5 (Fallen Warrior)}}

Mr. Weasley seems to be saying that wizards in general (of any age) can do instinctive magic in pressured situations, and that it’s especially common with children who aren’t trained yet. So, it seems that adults can do instinctive magic, but it’s more common in children.