Several young players who have played in the Olympics went on to become superstars in the past...
Football in the Olympics is not played at a senior professional level as teams are allowed to field U23 players thus making it a youth competition. Only three players over the age of 23 are allowed in the squad.
The U23 rule has been in place since the 1992 Barcelona Olympics. A primary reason why the football competition was converted into a U23 affair so that to avoid competition with the World Cup which is the biggest tournament in football.