Past condition - Is it grammatical?

Yes, it is grammatical. In English, the subjunctive is almost never used or understood any longer by English speakers. So, i might write: "If he were clever enough, he would have invested in Shanghai markets in 1990." Most native speakers of English would not recognize the subjunctive, and not understand why i wrote "If he were . . ." Most of them would write "If he was . . ." And, since language follows usage, that can be considered correct. Personally, i use the subjunctive, and often in response to the conditional, because i was taught about it when i was a child (almost 50 years ago). Most modern students in English-speaking countries either aren't taught about the subjunctive, or don't remember it, because they never hear it used.

By the way, technically, the past subjunctive, third person singular of "to have" is "had." So the sentence is also correct in the sense that the subjunctive in this case is not different from the simple past.

Could I ask more?
Is the following sentence also grammatical for the same reason mentioned by you?

If I had a million dollars in 1990, I probably would be a very rich man now.

(Somehow, I sense there's a difference

Yes, it is grammatical, and no, there is no difference.

One of the problems is that there is often no difference between the conjugation of a verb in the present, and the simple past, than there is in the conjugation of the same verb in the subjunctive, and the past subjunctive. It is most noticeable in the verb "to be," when "were" is used for the subjunctive in the singular person:

I was (simple past); i were (subjunctive and past subjunctive)
he (she, it) was (simple past); he (she, it) were (subjunctive and past subjunctive).

(The second person singular--thou, thee, thy and thine--is now never used.)

Since in almost all cases, the subjunctive form of a verb is no different than the simple past, many native English-speakers don't recognize the subjunctive when it is used, and if they see written or hear someone say: "If i were . . ." they just consider it incorrect. For all practical purposes, the subjunctive has ceased to exist in English.

Thank you Setanta very much! Your response speed is AMAZING!!


PS: I wish I can pronounce your nickname correctly. Is it /siTANte/?

Pronounce it: seh-TAN-tah.

All of my ancestors were Irish. The great mythological hero of Ireland was Cuchulainn (although pedantic university scholars argue of the pronunciation of that name, the Irish say: koo-KUH-lehn), which means "the Hound of Culain" (Culain is pronounced "KUH-lehn). But his name before he got that name, was Setanta. Below is a link to the story of how Setanta became Cuchulainn. It is a child's version of the story, but it is short and sweet, so you can quickly read and understand it:

The Legend of Cuchulainn--click here.

Setanta/Cuchulainn figures prominently in the greatest legend of Irish mythology, The Cattle Raid of Cooley, which in Erse (Irish Gaelic), is Táin Bó Cúailnge (Chain voh KOOL-nee). If you click here, it will take you to a page which has links to various versions of the legends which surround Setanta/Cuchulainn, and The Cattle Raid of Cooley.

Thanks A LOT for your explanation and the links!!!

Have a nice day!



Blues

The story is simple. Yes, I can read it.

Setanta is a man/boy's name. I used to take it as a lady's name.

What an ass I was

Not at all . . . you're not the first, and probably won't be the last, person to assume that it is a woman's name. In many European languages, words and names which end in "a" are feminine. Don't worry about it.

You are so kind!
Thank you again!