[Eph 3:21 KJV] 21 Unto him [be] glory in the church by Christ Jesus throughout all ages, world without end. Amen.
[Eph 3:21 mGNT] αὐτῷ ἡ δόξα ἐν τῇ ἐκκλησίᾳ καὶ ἐν Χριστῷ Ἰησοῦ εἰς πάσας τὰς γενεὰς τοῦ αἰῶνος τῶν αἰώνων ἀμήν
In concept, this may be an allusion to:
[Isa 45:17 KJV] 17 [But] Israel shall be saved in the LORD with an everlasting salvation: ye shall not be ashamed nor confounded world without end.
Isa 45:17 Masoretic: יִשְׂרָאֵל נֹושַׁע בַּיהוָה תְּשׁוּעַת עֹולָמִים לֹא־תֵבֹשׁוּ וְלֹא־תִכָּלְמוּ עַד־עֹולְמֵי עַֽד׃ פ
Isa 45:17 mGNT: Ισραηλ σῴζεται ὑπὸ κυρίου σωτηρίαν αἰώνιον οὐκ αἰσχυνθήσονται οὐδὲ μὴ ἐντραπῶσιν ἕως τοῦ αἰῶνος
Isa 45:17 Brenton LXX: Israel is saved by the Lord with an everlasting salvation: they shall not be ashamed nor confounded for evermore.
However, Paul may be alluding to a more specific reference, though again the wording is pretty different:
[Psa 119:90 NLT] 90 Your faithfulness extends to every generation, as enduring as the earth you created.
WLCלְדֹ֣ר וָ֭דֹר אֱמֽוּנָתֶ֑ךָ כֹּונַ֥נְתָּ אֶ֝֗רֶץ וַֽתַּעֲמֹֽד**׃**
LXX εἰς γενεὰν καὶ γενεὰν ἡ ἀλήθειά σου ἐθεμελίωσας τὴν γῆν καὶ διαμένει
Is he saying that the physical heaven and earth will go on forever or something else?
Possibly related:
[Ecc 1:4 KJV] 4 [One] generation passeth away, and [another] generation cometh: but the earth abideth for ever.
1:4 דֹּור הֹלֵךְ וְדֹור בָּא וְהָאָרֶץ לְעֹולָם עֹמָֽדֶת׃
1:4 γενεὰ πορεύεται καὶ γενεὰ ἔρχεται καὶ ἡ γῆ εἰς τὸν αἰῶνα ἕστηκεν
[Gen 8:22 KJV] 22 While the earth remaineth, seedtime and harvest, and cold and heat, and summer and winter, and day and night shall not cease.