Was Ganesha elder to Kaartikeya?

The order in which the literature came into existence in India is as follows;

Vedic Literature -> Srimad Ramayana -> Mahabharata -> Puranas

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1.   There was a reference to Ganapati in Vedas

गणानां त्वा गणपतिग्ं हवामहे कविं कवीनामुपमश्रवस्तमम्। 
ज्येष्ठराजं ब्रह्मणां ब्रह्मणस्पत आ नः शृण्वन्नूतिभिः सीद सादनम्॥

Except this mantra there was no other reference to Ganapati in Vedas - Rg Veda 2.23.1.  Scholars explained it does not refer to the Son of Uma that we are all accustomed to, but to Brihaspati.

https://in.answers.yahoo.com/question/index?qid=20110312035949AARJm3P

2.    in Srimad Ramayana, there was no mention about Lord  Ganesha and his First Adoration in Pujas.  Only mention about Kaartikeya  was made in Aranya Kanda.  The story of Lord Ganesha might have been  made in Puranaas, which were written at a much latter period.

While  roaming in the Dandaka Aranya, Sri Rama, Lakshmana, and Seetha enter  the hermitage of Sage Agastya.  While going to meet the Sage, they saw  the designated places for various Devatas.

स तत्र ब्रह्मणः स्थानम् अग्नेः स्थानम् तथैव च || 
विष्णोः स्थानम् महेन्द्रस्य स्थानम्  चैव विवस्वतः |
सोम स्थानम् भग स्थानम् स्थानम् कौबेरम् एव च || 
धातुर् विधातुः स्थानम् च  वायोः स्थानम् तथैव च |
स्थानम् च पाश हस्तस्य वारुणस्य महात्मनः || 
स्थानम् तथैव गायत्र्या  वसूनाम् स्थानम् एव च |
स्थानम् च नागराजस्य गरुड स्थानम् एव च || 
कार्तिकेयस्य च स्थानम् धर्म स्थानम् च पश्यति |  (Aranya Kanda 12th Sarga 17 - 21 Slokas)

Sri Rama entered inside the hermitage and saw therein the sanctus of  Brahma, Fire-god, Vishnu, Indra, Vivasvat  - the Sun-god, Soma - the Moon-god, Bhaga - one among the twelve Suns,  and the sanctusms of Kubera,  [Wealth-Management-god, are seen and passed by the three of them,  sanctums of Dhaata, Vidhaata - Vedic  deities created by Brahma to help Svayambhuu Manu, santucm of Vaayu -  the Air-god, and also like that  the sanctum of great-soloed VaruNa - the Rain-god who also wields noose,  and the sanctum of Gayatri  - the presiding deity of gnosis, sanctum of Vasus - eight of them, and  the sanctum of cobra's king -  aadi sheSa, the divine Thousand-headed serpent that bears this globe on  its head,  and even the sanctum of GaruDa - the Divine Eagle , and the  half  brother of aadi sheSa, and the sanctum of Kaartikeya - chief of gods army, and  the sanctum of Dharma - Dharmaraaja, presiding deity of Virtue-Vice-Time of living beings, in-charge  of the hell.

3.  Though Ganapati makes appearance  in Mahabharata (opening chapters), he was not mentioned further.

4.   It was only in Puranas that we will find elaborated stories of Ganapati, the son of Uma.  He is not a Vedic deity.  This story might be a fabricated one, replacing original Brihaspati.