Here's Nimoy at about 21 years old, about the same as Quinto was when the movie was being made. Not 100% on the exact year of the second pic.
When the movie was made Quinto was 31(!) not 21. When Nimoy was first cast for Star Trek he was 34. This is a mere 3 year difference which is clearly not significant. The fact that people whould assume Quinto is this much younger says a lot.