Gravitas means you have weight. People tend to conflate it with somberness and over-seriousness, but the men who have the most gravitas usually have an equal amount of charisma.
But true fathers have gravitas. They have a weight that attracts and influences. If you want to have influence on your children, and on others around you (including young men who are looking for good models of fatherhood), then you need to cultivate and promote your own gravitas.