Hmm, i checked a few obvious candidates on pro-football-reference.com.
Assuming Hopkins achieves the milestone this weekend, it looks as though he'll be the youngest.
Hopkins: 7 seasons + 15 games, 125 total games, age: 28y 203d
Rice: 7 seasons + 13 games, 121 total games, age: 30y 54d
Moss: 7 seasons + 15 games, 124 total games, age: 28y 315d
Fitz: 8 seasons + 6 games, 130 total games, age: 29y 44d
Are there any other candidates worth checking?
...dave