The use of "some" in those sentences is deliberately noncommittal.
It means that the speaker has either forgotten or does not wish to state how long ago.
In other words, the speaker is evading the question of how many years exactly.
Depending on the context, they may be implying that it is a sufficient number of years for making some particular judgement about the person they are talking about.
"I have known the defendant for some time and he is not the sort of person who would steal a policeman's helmet."
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Checking more dictionaries might have helped: 4
A considerable amount or number of: 'I’ve known you for some years now' Source: Oxford Dictionary Online 3.
Being a considerable number or quantity: '
She has been directing films for some years now.'
Source: American Heritage Dictionary B adjective II.
With plural nouns 8.
A certain number of; a few at least Or: at least a few b
In adverbial expressions of time. '
We shall meet some months hence' '
He has been here some years' Source:
Oxford English Dictionary
In general, in this context, some serves like a plural indefinite article.
Thus the use of some does not give a definite number.
But in time expressions, the OED says it means at least a few .
That is vague.
And that is what indefinite means.
The OED mentions for usage with singular nouns that some frequently implies 'not a little, considerable'.
And the other dictionaries back this up.
As other answers here have said or hinted, it often means: long enough! :)
A mother with a kid who is five would not say that her kid has played for some years with the next door kid who is also five.
That doesn't fit.
A teenager would probably not say that she has known someone for some years now .
Some does not fit the context.
As another answer has hinted or stated, the very word years means that a person has to be old enough to mean at least a few and imply a considerable amount .
In sum, the collocation some years does not at all mean a short time .
ell.stackexchange.com/users/27803/GoDucks
Some can mean both large and small amounts depending on the context in which it is used.
Consider these examples: A majority of persons were in favor of the vote but some were against it.
I have not read all of his books
but I have definitely read some.
Some villages in this state frequently experience flooding.
The meaning of some and subsequently the meaning the sentence conveys is different in all of these sentences.
In your case, it will mean the speakers have known each other for a good number of years .
They have not known each other since their beginnings, for, in that case they would have said
We have known each other since forever Or We have always known each other .
ell.stackexchange.com/users/12071/Mamta D
"Some" you should think of as "undisclosed amount", with a connotation of little or a lot depending on context.
"I found some money" might mean you found $1, or maybe $1,000,000.
However typically you probably mean closer to $1.
"Can I have some more?"
typically only means "can I have a small to moderate amount more?".
If you were served a plate of a food, and you asked for "some more", they would give you a second plate of equal or lesser amount.
"I have known him for some time"
typically only means "a long time".
You can think of this as "I have known him for a more than adequate enough amount of time to make whatever statements I made about him credible".
To copy another example: "I have known the defendant for some time and he is not the sort of person who would steal a policeman's helmet.
"
This should be read as "I have known the defendant for a long enough time to know that he is not the sort of person who would steal a policeman's helmet."
ell.stackexchange.com/users/None/
First off, we must bear it in mind that we are talking about the use and the sense of the determiner some in front of time, hours, months, years, etc.
According to The Free Dictionary, you use "some" with "time" and words such as hours, months, years, etc.
to refer to a fairly long time.
For examples: You will not be able to drive for some time after the operation.
We've been here for some hours now.
On the other hand, when you refer to a short period of time, you don't use some.
Instead, you say a short time and use "a few" in front of hours, days, months, years, etc.
For examples: Her mother died only a short time later.
You'll be feeling better in a few days.
In addition, you van use the phrases "some little time", " some few hours, months, years", etc.
to mean a short petiod of time.
For examples: Her mother died only some little time later.
You'll be feeling better in some few days.
However, if you want to refer to an unidentified or unknown time, you can use "some" before time.
For examples I saw him some time/sometime last summer.
We'll see some some time again, I am sure.
So whether some time means an identified time or a considerable/long time depends on the context.
As for "some years" in the sentence "We have known each other for some years" means a long time; a lot of years.
ell.stackexchange.com/users/9259/Khan
The definition of 'some' reads as  on OALD page   (#3)  a  large  number or amount of something   But then the next entry says...   (#4)  a  small  amount or number of something   I wonder if someone says ...   We have known each other for  some  years now   Or    I met him  some  years back   What about that 'period' that 'some' mean? Long or short?
"We have known each other for some years now" - so is it a long time or short time?
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<word-usage><word-meaning>
ell.stackexchange.com/questions/70385
ell.stackexchange.com/users/3187/Maulik V
"We have known each other for some years" means a long time - for many years. It depends on the context whether this refers to a short or long period.
It depends on the context whether this refers to a short or long period.