Games know no age, especially as the average gamer is in their mid-30's & Nintendo still holds the majority stake in the portable gaming market (although the mobile market has cut into their share).
Nintendo tends to be the family-friendly for their own games, which can potentially give off that "kiddie" vibe... but they have a solid collection for 1st party franchises that are virtually timeless (much like Disney's classics) while maintaining a modern appeal.
* Legend of Zelda: Breath of the Wild, Super Mario Odyessy, Xenoblade Chronicles 2 & Mario + Rabbids are couple of examples of great 1st party titles that you won't get anywhere else.
* Elder Scrolls V: Skyrim, Rocket League, Doom, L.A. Noire, The Binding of Isaac: Afterbirth+ & FIFA 18 are a few examples of major hits that can be easily taken on the go... although I'll admit this list is a bit heavy on the M-rated titles. I will note that Rocket League includes local multiplayer (each player can utilize one JoyCon) & CROSS-PLATFORM multiplayer w/ PC & XBox One players.
* Stardew Valley, Axiom Verge, Retro City Rampage DX & Shovel Knight: Treasure Trove are some major indie titles that be taken on the road as well.
* Some of the major sports titles (like FIFA18 & NBA 2K18) have returned to Nintendo. Only time will tell if all of them (like the Madden NFL series) will see a Switch release.
Your father may currently have a narrow view on Nintendo, but he may turn around as he likely sees more games on it that appeals to him (& you could tease him a bit with his originally narrow view later).