My son was born September 2007. For a flight from India to the USA on Virgin Atlantic, will he be issued a child ticket fare?
Typically the child needs to meet the age condition the time of boarding. If your son is not 12 yet on the day of your return flights, you can buy a child ticket. Otherwise you need to go with a young adult ticket.
Things are more complicated if the critical birthday happens during the travel. In this case you should contact the airline directly and ask for advise.
There doesn't seem to be much of a price difference, so I don't think it may be safer to just go with young adult.