Are there any American idioms for “learning something at young age otherwise it will hard to learn at older age”.

I know some idioms like you can’t teach new trick to old dog but it does not suit for the situation.

Question

Are there any American idioms for “learning something at young age otherwise it will hard to learn at older age”.

I know some idioms like you can’t teach new trick to old dog but it does not suit for the situation.

Answer

As an American, the idioms I'm aware of is:

"You can't teach an old dog new tricks."
"Old habits die hard."

Answer

It's not true. That explains why there are no such famous sayings, at least that I know of - because it's false. There are plenty of sayings that say the opposite though. For example,

The first half of my life I went to school, the second half of my life I got an education.
- Mark Twain

Answer

Our best and, as far as I know, *only* idiom for the idea you mention is, "you can't teach an old dog new tricks".