user19877: Who is the oldest person to become a GM via norms and hitting 2500 in rating? In other words, the standard way that most GMs achieve the title.
This would rule out any of the old masters pre-FIDE, and I also want to rule out those, who become a GM directly as a result of winning the World Senior Championship (like GM Larry Kaufman, for example).

user4418: The oldest player for whom I can find supporting evidence is Nikolai Shalnev who was 57 when he got his third GM norm in the Spring 2001 tournament in Odessa at which point his FIDE rating was 2550.
According to his (German) Wikipedia entry:

Shalnev trägt seit 2001 den Großmeister-Titel. Die dritte Norm für
  den Titel des Großmeisters hat er beim Turnier Spring 2001 in Odessa
  erfüllt, wo er mit 9,5 Punkten aus 12 Partien siegte.

Translated:

Shalnev has the Grandmaster title since 2001. He obtained the third grandmaster norm in the Spring 2001 tournament in Odessa, which he won with 9.5 points out of 12 games.


19877: <p>Who is the oldest person to become a GM via norms and hitting 2500 in rating? In other words, the standard way that most GMs achieve the title.</p>

<p>This would rule out any of the old masters pre-FIDE, and I also want to rule out those, who become a GM directly as a result of winning the World Senior Championship (like GM Larry Kaufman, for example).</p>
 4418: <p>The oldest player for whom I can find supporting evidence is <a href="https://ratings.fide.com/card.phtml?event=4146042" rel="nofollow noreferrer">Nikolai Shalnev</a> who was 57 when he got his third GM norm in the <a href="https://ratings.fide.com/individual_calculations.phtml?idnumber=4146042&amp;rating_period=2001-07-01&amp;t=0" rel="nofollow noreferrer">Spring 2001 tournament</a> in Odessa at which point his FIDE rating was 2550.</p>

<p>According to his <a href="https://de.wikipedia.org/wiki/Nikolai_Shalnev" rel="nofollow noreferrer">(German) Wikipedia entry</a>:</p>

<blockquote>
  <p>Shalnev trägt seit 2001 den Großmeister-Titel. Die dritte Norm für
  den Titel des Großmeisters hat er beim Turnier Spring 2001 in Odessa
  erfüllt, wo er mit 9,5 Punkten aus 12 Partien siegte.</p>
</blockquote>

<p>Translated:</p>

<blockquote>
  <p>Shalnev has the Grandmaster title since 2001. He obtained the third grandmaster norm in the Spring 2001 tournament in Odessa, which he won with 9.5 points out of 12 games.</p>
</blockquote>
