Short answer: in Jain Dharma there is no religious barrier to a Jain boy marrying a Jain girl who belongs to any caste (including a Brahmin caste if she is a Jain). What matters is both partners are Jains themselves and willing to follow Jain conduct and rituals.

More precisely:

• If both partners are practicing Jains, the marriage is considered acceptable. Varna or caste (e.g., Brahmin) is not a doctrinal obstacle in Jainism; what matters is shared commitment to ahimsa (non-violence), truth, and Jain ethical duties.
• If the Brahmin girl is Hindu and not Jain, many Jain families and priestly authorities would typically advise caution. Interfaith marriages are not forbidden in all Jain groups, but they are less common and can require careful discussion, mutual respect for each other’s dharma, and personal decisions about how to observe Jain practices in the home. Some families may prefer both partners to be Jains.
• There are differences between Digambar and Shwetambar traditions in various customs, but neither tradition imposes a hard doctrinal ban on a Jain marrying someone from another caste or from outside Jainism, provided both partners adhere to Jain values.

Practical steps you might consider:

• Talk openly with family elders and a trusted Jain priest to understand the local customs and guidance.
• Ensure both partners are comfortable with Jain rituals, dietary rules (e.g., ahimsa, vegetarianism), and daily practices.
• If there’s a difference in faith, discuss how ceremonies, naming, and prayers will be handled in the home.

If you’d like, I can help you find a relevant JainKnowledge page that covers Jain marriage customs or the views of Digambar/Shwetambar communities.