Wow, i din't know those stats, but very interesting ones they are too.
Maybe they go a bit hand in hand as well, a lack of experience causing defensive frailties which lead to more goals?
There is a distict emphasis on attacking football and philosophy too in the Eredivisie rather than the safety first approach seen elsewhere in Europe, great and entertaining to the supporter, neutral or otherwise.
Also maybe there in an imbalance between the good and not so good teams here, hence you might get more 4-0 5-0 victories than in say England where even the bottom feeders can give the top clubs a scare every once in a while even if they eventually lose the games.
Great stats none the less and no wonder it is one of my main forms of entertainment every weekend, apart from yesterday afternoon!
Stats play a big part in my gambling process so quite sadly I know way too much!
And yes, one could argue that there is a correlation between average age and average goals per game. Leagues that consistently have the lowest goals per game average such as Russia, Romania, Greece, and Italy tend to always also in the top 6-8 for highest average age. There are of course exceptions - England and Spain are often in the top 5 for highest average age, but also in top 5 or 6 for highest goals per game.
And you only have to look at how the B teams/reserve teams play in the professional leagues to realise that the younger the team the more goals are likely to occur. For instance, Real Madrid Castilla and Barcelona B both played in the Segunda division in Spain last season, both obviously had much lower average age than other teams, and also were both. And I expect Jong PSV, Jong Ajax, Achilles etc.. will also be near the top in Eerste Divisie come end of season for average goals per game.
There are certainly a lot of variables though. Like you say the imbalance or inequality in leagues can also play a part. You get teams like Real Madrid and Barcelona that average almost 4 goals per game (games involving Barca did average over 4 last season) which obviously bring up the overall average in the league as they each average almost 1 goal more than everybody else in La Liga!
Other variables include quality of the pitches/turf, the culture of the country and traditional aspect - for instance in Italy teams rarely kill teams off with big scores, there is almost a silent agreement that you don't disrespect the opponent by thrashing them 6-0!