"Help! My beard/hair is turning white."
May a man pull out the white hairs from his beard/hair?
Although Shulchan Aruch YD 182:6 forbids a man to do so, placing it in the category of "women's dress", he continues to forbid looking in a mirror as well.
A parenthetical notation (Rema?)is made following the mirror halacha sending you to YD 156 were the Rema quotes those who say that this law is dependant on whether men customarily look in a mirror or if this practice is exclusive to women.
This same distinction would apply to your case. Perhaps this was not mentioned because it was (possibly) illogical at the time to want to look younger.
(As usual, consult a competent authority.)
Here's a quote from Halacha for Today (Question 260):
Q: Could you tell me if it is permissible for a man to dye his hair?
A: A man may not dye his hair if doing so for beauty or to hide white hair etc. as this is a biblical transgression of "Lo Tilbash" not to wear (or otherwise imitate) the ways of the opposite gender. This includes dying hair, plucking out even one white hair for a man, wearing clothing of the opposite gender, men shaving areas of the body that are shaved generally by women, etc. These are very severe prohibitions and a Rav should be consulted to determine what does and does not fall into the prohibition of Lo Tilbash.
The Shaalos U'Teshuvos Minchas Shlomo (Chelek 2 Siman 82 Ois 7) discusses whether a man may have plastic surgery when it is being done due to discomfort rather than for beautification. For example if his nose is very unusual. The Minchas Shlomo writes that it is allowed. In addition he writes that for this reason it is permitted to dye or pluck white hairs for a young man where according to his age it is considered a deficiency, and his only reason he is doing it is in order not to have this deficiency.
This is discussed in Mesechet Makkot (20b approximately) - I believe in Rashi or Tosafot if not the Gemara's text itself - in the context of destroying your beard/hair. From a cursory glance, it's considered to be a violation of that commandment and if you were to do so, you would be liable to receive lashes, provided a correct warning and corroborated testimony, etc. Thus, it seems there is a good precedent for it to be forbidden either in the context of destroying your beard/hair or because of "beged isha", as other answers have covered.