Hi Richmond, 

What is the age of the passengers in this case? 
Interrail offers 1st class passes for youth (12-25 years).

And you can also get them for children:

Hi Richmond, 

What is the age of the passengers in this case? 
Interrail offers 1st class passes for youth (12-25 years).

And you can also get them for children:

 

Oh thank you so much for your reply. I am actually asking for business class not first class since I am travelling with my parents very soon and they are travelling by business class so I need information whether I can travel with them as a youth who is 21 years old. I don’t have children yet.

Trains in Europe generally only offer 1st and 2nd class. Eurail passes have the same distinction. A few railways companies have invented more classes, but that often comes down to 2nd or 1st class and some extras.

For the passes though, there is only a choice between 1st and 2nd class.

Hi Richmond, All passengers can travel with a 1st class pass, you can choose to do so when booking your pass. Cheers,

There can be some exceptions, like in the UK. There, children in the age of 0 and up to 5 can only take up a seat, until a paying customers need it. https://www.nationalrail.co.uk/times_fares/46494.aspx

“Please ask questions in the forum and not via a private message. That's the most convenient and quickest way to get a response.”

Can you kindly send me the link to Eurail forums

You are already on the forum.