Answer:
It's tough to be the youngest.
Step-by-step explanation:
The infinitive form of a verb is the verb in its basic form. It is most times started with 'to', and then the base verb follows. It could also simply just be the verb in it's base form. A gerund is the -ing form of a verb. So, in the sentence above, the gerund is 'being'.
Therefore, to convert this sentence to the infinitive form, the gerund, 'being' will be converted to its base form, -be. When 'to' is attached to it, it becomes the infinitive, -to be.