Does Brahma look like an old deity, having white hair? What is his body complexion - red, golden or something else. Does he use rosaries for chanting? If so then which rosaries does he use(rudraksha or tulasi mala)? Which type of tilak does he put on his forehead - urdhava pundra (u shaped tilak of Vishnu) or tripundra (three lined tilak of Shiva)?
To know how a deity looks like we need to look into that deity's Dhyana Shloka (also called Dhyana Mantra sometimes).
For Lord BrahmA, since his worship is prohibited, it's difficult to find a Dhyana Mantra. But I know about a DhyAna Shloka, that is quoted in the book Anhika Kritya (by Shyamacharana Kaviratna Varidhi); first BhAga; first Khanda; section-DhyAnamAlA.
And, it is as follows:
BrahmA kamandalu-dharashchaturvaktrash-chaturbhujah |
KadAchidrakta-kamale hamsArudhah kadAchana ||
Varnena rakta-gaurAngah prAmshustunganga unnatah |
Kamandalur-vAmakare sruvo haste tu dakshine ||
DakshinAdhastathA mAlA vAmAdhascha tathA sruchA |
AjyasthAli vAmapArshwe vedAh sarvehagratah stithAh ||
SAvitri vAma-pArshwasthA dakshinasthA saraswati |
Sarvve cha rishayo hyagre kuryadevishcha chintanam ||
Lord BrahmA holds the Kamandalu (a water pot); he is having four faces and four arms; Sometimes (he is seen) seated on a red lotus and sometimes on the Swan. His body is having an extremely stout structure and is having a reddish-white complexion. The upper left hand is holding the Kamandalu and the lower right hand holds the rosary beads; the lower left hand holds the Sruk (the laddle used while pouring the Havi in fire); the upper right hand is holding the Sruva (the utensil in which the Havi is stored);
On his left hand side is present the AjyasthAli (the plate that contains clarified butter or Ghee); in his front (are present) the Vedas; on his left is present SAvitri and on his right Saraswati and in his front are present all the Rishis. One has to meditate upon Lord Brahma in this way.
So, it does not specify if Lord BrahmA is having white hair and white beard or not. Also, although it specifies that he carries a JapamAlA, but it does not specify what kind of beads (like RudrAksha, Tulasi or any other) that MAlA is made of. And, regarding the Tilaka on forehead, it has no information.
I have also consulted the Deva Kritha Brahma Stotram found here but it is not of any help regarding finding out details of Lord Brahma's physical appearance.
Similarly, I have also checked the Brahma Stuthi Panchakam. But it too does not provide any additional information.