new neighbour speaking to me like I am an idiot

Haha, agreed.

I would amp it up

She is just a passing neighbour why do you even care?! 🤷‍♀️

You could say to her 'could you repeat that, dear?'

Do it about 3 times

What ages are you? 40 and 50 or 80 and 90?

I’d drop something in to the conversation to alert her to your ability to be a high functioning adult. ‘Oh I was just reading about developments in data governance. I was CEO of the ICO before I retired and maintain an interest’.

Pardon? Are you saying people in the UK are so bigoted and ignorant that they talk down to Americans as standard?

Why bother talking to her at all? When you see her coming, turn and walk away. If she ambushes you, look at her blankly then turn and walk away.

Do let her see you chatting to other neighbours and people if possible though. No reason to have any conversations with rude people.

If she is patronising, you must ask yourself if she is the kind of person you want to have a conversation with, apart from the neighbourly basics of Good morning. We have new neighbours and I just say hello, nice day, or whatever. I don't get into any conversation. Like that you can address the big stuff if it happens without feeling you have to take a step back from friendly boundaries.

Your spelling of realise and recognise suggests that you may be American. Are you living in the UK? If so, it may not be your age behind speaking to you that way!

Are you sure she doesn’t talk to everyone like that?

I imagine she's trying to be caring. I think I'd probably just say something. Or avoid her. I have said to someone, I'm 50, not 90 you know. I think some people have an imaginary line which divides young and old in their head.

Agree - Have fun with it - Maybe 'accidently' wander in to her kitchen & sit down innocently waiting for dinner?? Ask her to help search for your (imaginary) cat?
Speak about things like 'in the olden days'...(1980s)....eg when you were a dancer on Top of the Pops.... - then get genned up & ask questions about current political policies, rubbish current TV, oh and ask for advice about pensions for when you are old enough, or what you should do with all your money?

Invite her to the private rave next week?

But, I am pretty sure that when I was about 20, I thought that being about 40 was ancient 🙂- so maybe do all tongue in cheek, then kindly let her know & hopefully have a little giggle with her?
It doesn't sound like malice is intended, from what you have said so far?
(Or, if it is malicious, ask what face cream she uses as you have been told that you look younger than her (that maybe a 'lil bit brutal though, Hmm depends....) . XX 😉🌹

Ignore her.

Unless you can give an actual example, she might be right

OP examples are needed. Because either she does speak to you like that or you’re the one projecting something. Hard to tell.

I’d be tempted to say ‘Oh no, it’s fluffing you again’! But if someone is patronising or rude to me, I give them a dose of their own medicine. It makes me smile!

“And forgive us our trespasses, As we forgive them that trespass against us”

One of the nearby neighbours ( our street curves round ) keeps saying “ oh bless “ I feel likes she is being patronising as if I’m a dotty tiny old lady .
it Is annoying

OMG? Literally the worst advice given. Ever. In the history of advice.

Translated your advice reads as: Just put up with it because it might cause some offence or some uncomfortable feelings. Seriously who gives that as advice? 🤦‍♀️

Don’t speak to her then 🙄

Yeah, exactly. I used to work on an activist project with someone with a deeply peculiar manner, who called everyone 'darling' in a strange, preoccupied staccato way, sometimes several times in a single utterance, whether they were staff, friends, the general public, and managing to give the general impression she was just too busy and important to remember your name. But she did it to everyone. I recently saw her on a TV programme about house restoration, and she was still at it, 'darling'-ing everyone from the presenter to the builders to some local historian.

It is annoying, a friend of my mum (30’s), was calling my mum elderly when she was in her mid 50’s.

Drip feed! 😂

I know a couple of people who do this. I feel a bit sorry for them but I would never bring it up because that would be a bit mean. Presumably they can’t really help it.

It's probably her default setting. I don't really know why you'd be that bothered, or thinking of confronting her about it. She's not your friend, she's just a neighbour. You don't have to say more than hi and bye to her.

I can see why this would be a huge deal to you if she was, eg, your SIL or your boss, but she's literally just someone who happens to live down your street, who you find mildly irritating. That's all. Sometimes people will have a natural manner that slightly annoys us; that's life.