Hi
It’s about time… and It’s high time…
are standard expressions.
It’s high time you… [sold your car / started to do exercise / behaved yourself 
/ whatever…]
But, to be honest, I always see and hear the phrases with you
and now can’t find which one is right:
It’s high time her/him …
or
It’s high time she/he …
Or they just can’t be used that way?
A subject pronoun is needed here: It’s about/high time she/he did something about it.
But: It’s not too late for her/him to do something.
Tamara
You can’t use an object pronoun there but you can use the possessive form, which of course is the same as the object form for females.
It’s high time her/his mother taught her/him some manners.
Thanks!
…Correct using of subjunctive (?) forms (especially with Past Participle) is still a real challenge for me…