As the question says, are there any taboos/guidelines or any references to authoritative texts or incidents where a younger groom marries an elder woman?
Yes, there is a scriptural basis for the restriction.
Here is what Krishna says to Uddhava in the eleventh chapter of the Uddhava Gita of the Srimad Bhagavatam:
One who desires to establish family life should marry a wife of his own caste, who is beyond reproach and younger in age. If one desires to accept many wives he must marry them after the first marriage, and each wife should be of a successively lower caste.
As it is already said in above answer that marriage between elder bride and younger groom is restricted but for answering the second part of this question that asks for the reference of such marriage, there is a very famous example of marriage between Lord Balarama and Revati is described in Bhagavatam here where Lord Brahma says following words to Kakudmi (Revati's father):
gotrāṇi ca na śṛṇmahe
kālo ’bhiyātas tri-ṇava-
Twenty-seven catur-yugas have already passed. Those upon whom you may have decided are now gone, and so are their sons, grandsons and other descendants. You cannot even hear about their names.
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.
It is said that a man shall marry a maiden who is much younger than him.
See about that in the Vishnu Purana: Book III: Chapter X:
"If he marry, he must select a maiden who is of a third of his age"