User experience / interaction design for elderly people using banking apps

In regards to "tweaking the standard". If we are talking about mobile apps the "standard" tends to be that particular OS' guidelines.

In both the case of Apple iOS14 and Material design, the majority of the components, size of the buttons for touch, standard text sizes etc have been defined so the majority of users can experience no issues using the mobile device.

However, in your question you're talking about "clutter" and too much information. This sounds more of a case of showing too much content to the users rather than using the wrong design components.

I would recommend you look into things like Progressive Disclosure and the 10 UI Heuristics as points of reference that might help you display content in a timely and helpful way.

Lastly, and this might be more of a dev point rather than a design one, ensure that your app supports the native OS' accessibility settings.

A lot of older users tend to opt for larger text, contrast options, or even screen-reading for their devices. Ensuring your app can still function, navigate, and display content properly with users that may have altered those settings will definitely improve the usability for quite a few of your elderly users.

Firstly you need to define 'older people': 80 year olds will behave differently from 40 year olds.

Eyesight starts to decline during the 40s decade: so you'll get 48 year olds complaining about the text being too small.

( people who haven't been lifelong glasses wearers tend to put off wearing glasses as their eyesight gets worse, they'll blame the interface rather than give in to glasses !)

So 40 somethings are 'older people'.