As you can imagine different fitness goals will require varying commitments to training. However in general:

To Maintain General Health

As a minimum it is recommended to weight train at least twice a week. If you choose to train only twice a week, a full body workout would suit this well.

Sweet spot

For the majority of the population who want to be able to maintain a balanced lifestyle, make gains and also recover sufficiently, the sweet spot for weight training would be 3 sessions per week. Given that a great session can be completed in 45-60 minutes, this only amounts to a time commitment of 3 hours a week. When you think about this only being less than 2.5% of your week, this is one of the best time investments you can possibly make

Fitness Model / Bodybuilding

The reality is if you want the body of a pro fitness model or bodybuilder you'll have to train at least 5 days a week, and also hope you have won the genetic lottery. Rarely will you find any top level physiques who weight train less than 5 days a week, and this does not even include cardio sessions. When you factor in additional cardio before competitions and photo shoots, some fitness professionals can be in the gym for over 15 hours a week.

In all cases there will always be a few exceptions, the important thing to remember is that goals can change, and you don't have to stubbornly stick to the same routine for years.

Progressing is always more difficult than maintenance. So perhaps a younger, single you was able to train 6 days a week to reach your ideal physique, but now you can happily maintain on 3 sessions a week and consistent, good nutrition. Always have a goal in mind, and you'll have a lot better idea of what training and nutrition needs you have to achieve this goal.