Limit number of selected entries from a dropdown for a date

Hi, I have booking form with dropdown for the number of people and two date fields for a dates('from' and 'to'). In the dropdown the choices are 1, 2,3,4,5,6,7,8,9,10.  Can I set so the maximum capacity is for example 20 people.  So if a customer is trying to book a travel on a date where there already is 20 people they get a some massage for example ”Unfortunately, it is already fully booked”. Or to count the people per travel date and disable that date (grey-out) in the dropdown if the maximum has been reached. Thanks.