Hi,
Unless you know what is causing the vomiting I would have him seen tonight if possible. Dehydration can happen very quickly in cats, especially in older cats, and the more he vomits the more likely dehydration is going to be a problem. If you have access to an emergency clinic Iwould have him seen right away. At 10 years old, it would be much better safe than sorry.
I hope this helps. Please let me know if you need additional information.
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