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.
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.
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.
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"
Sanathan Dharma avoided marriage between younger groom and elder woman and allowed marriage only between elder groom and younger woman.
While listing the duties of a householder, Yajnavalkya told that wife should be younger than husband.
The wife should be a, girl young in years and not previously married to any other husband, in the possession of sound health and having had uterine brothers of her own, and not related to him by any tie of Sapinda relationship, nor belonging to the same spiritual clanship (Arsa Gotram) as his own. She should be taken from any of the sixteen reputed families of the rotriyas, not related to the bridegroom within five and seven degrees in the lines of his mother and father respectively.
It has been mentioned that one should avoid intercourse with elder woman. We can understand that marriage should be avoided.
The six things, such as the use of a new wine or Trimulakam (lit., horse radish in its three different forms) the partaking of curd in the night, or of dried meat, sleep during the, day, and the bed of an elderly woman, should be abjured.
Intercourse with elder women is an depletive agent that reduce strength and vitality of the person.
Dried meat, exposure to the rays of the autuman, sun (in Virgo), curd of more than two days manufacture (Tarunam Dadhi), intercourse with a woman older than one's own self, and sleep and coitus in the morning are the six depletive agents that tend to reduce strength and vitality. coitus in the morning are the six depletive agents that tend to reduce strength and vitality.
It has been mentioned multiple times across the scriptures to avoid marriage with women who is older than the groom.