(I assume here that Acts is historically worthless regarding Paul's chronology, but that the reference to king Aretas in 2 Corinthians dates Paul as a young man no later than to the year 40.)
The subject in Romans 9-11 is Paul's "great sorrow" and "unceasing anguish" over the people of Israel, his kinsmen according to the flesh. What is he so sad about? Some large number of them have been rejected and punished by God. In 11:16-24, he speaks of a number of "natural branches" of the orginal vine, the people of Israel, being broken off, because of their unbelief.
The conventional (i.e. Christian) view is that Paul is referring to the events of salvation history as he has always understood and proclaimed them as God's apostle: that (a) a new covenant has been made by God with all people, Jewish and gentile, through faith in Christ; (b) this new covenant surpasses the old covenant (cf. 2 Corinthians 3:6-18)); and (c) many Jews (aka Israelites according to the flesh) have refused to believe in Christ, and so enter the new covenant and be saved. Essentially, Paul is sad for the Jews who reject Christ, because they reject Christ and are therefore condemned by God (damned in the afterlife, per Christianity).
But how do we know that Paul is not alluding to the events of 70?
It might be said that Paul refers to the temple worship in Jerusalem in 9:4, as though referring to an ongoing state of affairs--
But these are God's "once and for all" gifts to Israel, through the written Torah. The latreia (worship) does not have a definite reference here.They are Israelites, and to them belong the sonship, the glory, the covenants, the giving of the law, the worship, and the promises.
Perhaps a stronger argument can be made from Paul's silence. If he knew about the events of 70, you say, surely he would have much to say about them. But this argument fails because Romans 9-11 can be read exactly as that: Paul's lament for the sufferings of Judea (although he's no Jeremiah), and his theology of the extinction of 2nd temple Judaism. There may be an element of caution in not referring overtly to Roman emperors, armies, conquests, policy, etc. It is, moreover, typical for Paul to be vague about historical reference points.
The old branches were broken off "so that" (11:19) new branches (the gentiles) might be grafted in. And, "as regards the gospel, [unbelieving Israelites/Jews] are enemies because of you" (echthroi di' humas) (11:28). In these and many other passages, there is a strong suggestion that something momentous has recently occurred to "Israel according to the flesh." Their suffering has become part of salvation history in a new, unexpected way.
Do these passages really have nothing to do with the Romans, the destroyers of the temple, whose captive Paul is at the end of his life, and to whom (gentile believers in Rome) he is writing his magnum opus? And why else would he write so many dark passages about the wrath of God (1:18ff, 9:22, etc.), a theme that, although not absent from earlier epistles such as 1 Thess, is much more dominant here?