Unicorns can live forever but they remain children for 21 3/4 years. how many months is that?

255

Explanation:

261

Explanation:

There are 12 months in a year, so 12 times 21 would be 252 months. Then you would do 12 divided by four to get one fourth of a year which would be three times three because you need three fourths. That would be 9. Add those together and it's 261.