For people (like me) who recognized the name but didn't remember the details, he's the guy who came off the bench against Brentford, and ended up breaking the record for the youngest player to ever play in a competitive match in a top-of-the-pyramid match (i.e. Premier League and First Division before the Premier League existed). That record had existed since 1964.

At the time, he was 15 years and 181 days old. When Cesc Fabregas played his first League Cup game for Arsenal he was 16 years and 177 days old, almost a full year older. Even Messi only made his first Barcelona first team appearance at 16 years and 23 days, and that was only a friendly.

Nwanieri started playing with the U18s at 14, and the U21s at 15. Now the only step up possible at Arsenal is to play for the first team, and he only turned 16 3 months ago.

And, to make you feel old:

Nwaneri was born after:

Arsenal moved to the Ashburton Grove (sponsored by Emirates) stadum
Dennis Bergkamp retired at age 37
Twitter launched
YouTube launched
Italy won the 2006 world cup
The ROBLOX game was launched