How to politely decline an interview offer without burning bridges?

A person I met at the job fair recently contacted me for an interview. However, I now know that my schedule in the next year wouldn't allow me to have the room for more part time jobs (possibly it will be later next year when I will have the room). I really like the company though and want to work for it when the opportunity arises and my schedule is more free.

How should I send an email reply to the person to still show interest but let them know I won't be able to have the interview because I won't be able to work for them for (probably) the first half of the year? I don't want to burn bridges, and I don't want them to not consider me when I am able to work with them later down the road.

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