我有很少朋友的朋友很少，可是我有一个很好的朋友。

The phrase "我有很少朋友" is grammatically correct in Chinese and conveys the meaning that you have very few friends. However, it sounds a bit awkward and not very natural in Chinese.
A more natural way to express the same idea would be to say "我的朋友不多" (I don't have many friends) or "我的朋友很少" (I have very few friends). Both of these phrases are more commonly used in Chinese and sound more natural.

她是个好人。

小时候，我们一起过时间。

"小时候，我们一起过时间" is grammatically correct in Chinese, but it doesn't sound very natural.
A more natural way to express the same idea would be to say "小时候，我们经常在一起玩" (when we were young, we often played together) or "小时候，我们一起度过了很多时光" (when we were young, we spent a lot of time together). Both of these phrases are more commonly used in Chinese and sound more natural.

现在我能说：“他她是了我最好的朋友”。

"他她" is not commonly used in Chinese to refer to a specific person. Instead, you should just use "她" to refer to your female friend.

"她是了我的朋友" doesn't convey a clear meaning and sounds a bit awkward.
If you want to say "she became my friend", a more commonly used expression is "她成了我的朋友" (she became my friend), where "了" is used to indicate a change in the state of affairs. This conveys that your friend was not your friend before, but became your friend later.
If you want to express that your friend is your best friend, it's better to use "她是我最好的朋友".
I hope this helps!

可是在我的心里我们10岁。

"在我的心里我们10岁" (in my heart, we are 10 years old).

我有很少朋友的朋友很少，可是我有一个很好朋友。

她是个好人。

小时候，我们一起过度过了很多时间。

我们都很高兴了。

现在我能说：“他她是了她曾经是我的朋友”。

我知道那是我的最好的时间。

¶
现在我17岁，她也17岁。

可是在我的心里我们还是10岁。