That's completely wrong. If they were indeed 4 years older than Kakashi, they should have been a lot taller than him when they were part of Team Minato.
Anyway, it's not said exactly how old they are, but judging by the fact that most ninja students become a Genin or get graduated at the age of 12, and since these are the birthdays of the characters:
- Rin is born on November 15
- Obito is born on February 10
- Kakashi is born on September 15
there are some scenarios we could come up with (imagine the world of Naruto being 2005 and 2006):
All three of them are born in the same year, making them all the same age (12) and making their age order like this: Obito>>Kakashi>>Rin, making Obito 7 months older than Kakashi and 9 months older than Rin, while Kakashi being 2 months older than Rin.
They are born in different years: making it look like if Rin is born in 2005 and the other two in 2006, then it's Rin>>Obito>>Kakashi, making Rin only 13 years old, while Kakashi and Obito are 12, and are 10 months and 3 months younger than Rin, respectively.
If you mean the current timeline, obviously Rin is dead, but Kakashi was 26-27 years old in part 1, and 29-31 years old in part 2, same for Obito. This will automatically make Rin 29-31 years as well, if she was still alive.