I doubt their highest league would be pro. They would still have full time jobs. Not sure any European country has a "pro" league.
It's entirely possible a 19 year old could play 5 years in top division though. If he is a big kid and really talented he'd probably find a spot, but it would probably be with the junior team and not the senior team. Almost every club in Europe has at least 2 teams. an under 18 and a senior team. in some countries they have an under 21 division as well. each age group has to qualify for the division they play in. Think college division ranking.
the thing is that the top league in some countries would include every club that could field a team.