You know the rule: You shouldn't assume a poem's speaker is the poet. That being said, there isn't anything in "Oranges" that makes us think this isn't a recollection from Soto's youth. But let's focus on what we do know for certain about this speaker.
First of all, it's a guy remembering the first time he walked with a girl. We get a sense from the carefully remembered details ("newly planted trees," "the tiny bell," "a few cars hissing past") that this isn't an event that happened last year, or even in the last 10 years. This is something that happened long ago but was significant enough to make a big impact on the speaker. This means that our speaker is probably an older man, perhaps middle-aged, remembering his youth and his first love.
We also get the sense that this speaker a regular Joe. He isn't using a lot of fancy vocabulary or flowery language to describe his experience with the girl. (Heck, he doesn't even say the words "love" or "heart" and this is a poem about love.) We know the memory means a great deal to the speaker—not because of how linguistically elaborate or sentimental his descriptions are, but rather how accurate and sensory they are. The speaker recalls sights, sounds, and other sensations that help place the reader in the scene and also help transport the speaker back to that day with his first love—details that help the speaker, and the reader, experience those first love feelings again.
We get the sense that this speaker is a romantic kind of guy but not in a sappy, sentimental way. He's just a guy that recognizes important moments in his life and wants to hold onto them—like through this poem.