Any references to authoritative texts or incidents where a younger groom marries an elder woman?

Yes, there are few incidents of boy marrying girl older than him:

• As per Śrīmad-Bhāgavatam (Bhāgavata Purāṇa): Skandha 9: Chapter 3, Revatī was much (twenty-seven catur-yugas!) elder than Baladeva (Balarama). Brahma advised Revatī's father to offer his daughter to Balarama.

• As discussed in Was Radha aunt of Krishna? post, Radha was fourteen years elder than Krishna and Brahma had performed the marriage of Radha with Krsna (Brahmavaivarta Purana: Prakrti-Khandam: Chapter 49).

Also, as per SB 10.55, Kamadeva took rebirth as Pradyumna but his wife Rati started living as a cook in the household of Śambara with the name Māyāvatī. So Māyāvatī's body was much older that that of Pradyumna's.

Any references to authoritative texts or incidents where a younger groom marries an elder woman?

Yes, there are few incidents of boy marrying girl older than him:

• As per Śrīmad-Bhāgavatam (Bhāgavata Purāṇa): Skandha 9: Chapter 3, Revatī was much (twenty-seven catur-yugas!) elder than Baladeva (Balarama). Brahma advised Revatī's father to offer his daughter to Balarama.

• As discussed in Was Radha aunt of Krishna? post, Radha was fourteen years elder than Krishna and Brahma had performed the marriage of Radha with Krsna (Brahmavaivarta Purana: Prakrti-Khandam: Chapter 49).

• As per SB 10.55, Kamadeva took rebirth as Pradyumna. Māyāvatī's (Rati) used to live as a cook in the household of Śambara when Pradyumna arrived there as a just born baby. So Mayavati was much older than Pradyumna.