There's almost exactly 20 years between myself and my partner.  I ran away from home young to escape an abusive family situation so, at the time or relationship started, there was a world of difference in life experience between me and the boys my age. 

My partner and I have similar values and ambitions for life.  We have a similar level of education and earning potential.  We both have our own baggage from our families of origin.  For 10 years we've had a safe, stable, comfortable, loving relationship. We're a team and we're equals.

Meanwhile, THE boys my age (that I earned my degree with, or currently work with) are still thinking about playing video games all night, getting drunk and "scoring" at every opportunity - they're still not quite grown up enough for me.

I'm not saying that it's appropriate for a 42 year old to date someone 20 years younger than them. But it's not always inappropriate either.  Life experience and the relationship dynamic (especially if there's a power differential) are important to consider