You might be surprised to learn the level cap in Baldur's Gate 3 is just 12. A dozen level-ups across a roleplaying epic that will reputedly take completionists up to 200 hours to see everything it has to offer. For comparison, The Witcher 3 and Cyberpunk 2077 — perhaps the nearest RPGs in terms of size and scale — have level caps of 70 and 50 respectively, to give you an idea of how infrequently this will occur. As this is a party-based CRPG at its core, you'll be levelling up your Companions as well.
The reasons for this are based on the Dungeons & Dragons bedrock upon which everything stands. In BioWare's original Baldur's Gate (1998), you started the game as a nobody, easy prey for any passing pack of goblins alone. By the end of the game, you might be level 10, famous within the local region, and ultimately go on to save the titular city of Baldur's Gate from destruction.
Even though Baldur's Gate 3 has a level cap of 12, it's highly unlikely you will reach it unless you're a completionist. But don't worry: the experience of playing a character through the earlier Baldur's Gate series (including both game's respective expansions, Siege of Dragonspear and Throne of Bhaal) was one of the most satisfying and believable escalation not only in RPGs but in all gaming. It made players feel like their characters truly grew into legends, and Baldur's Gate 3 is aiming to do the same.