I'd like it if the word "elder" meaning "older" didn't exist. Then I'd assume it was after elderflowers / elderberries.
But since the "older" meaning exists and that would be weird for a name, I would use Alder instead. Alder has a similar sound, it's still a plant, and it doesn't sound like you're pretending your baby is an old person or a Mormon missionary.
(I didn't know about
Hélder until clicking the link to
Elder in this post, so that's why I only thought of the plant association and the word "elder").