Esa bicicleta es demasiado pequeña para ti.

English Translation

That bicycle is too small for you.

Anyone have any idea why it’s ‘demasiado’ and not ‘demasiada?’ shouldn’t the adjective agree with the noun, bicicleta??

The bicycle is too small for you.

The main word describing the bicycle is small. The role of too is to describe small which makes it an adverb. In Spanish, since adjectives don’t have an inherent gender adverbs remain unchanged. Here’s a few other examples:

demasiado caro; demasiado alto; es demasiado introvertido; vivimos demasiado lejos.