In American English we would use 'is' with a collective noun such as 'generation'. In British English, 'are' is often used for collective nouns. Both are acceptable.

I would say 'younger generation' rather than 'new generation', 'main' instead of 'major', and 'for' sports goods : 'The younger generation are the main customers for sports goods.' However, in a formal context, e.g. a report, Migee's version [above] is more appropriate.

The first sentence is correct but you can change the word "customer" to "consumer" if you want it to be on an economic stand point :) The new generation is the major consumer of sports goods.

The first sentence is correct