My kids, are very big for their ages, not in girth, but in height. And they are very lean and have good percentages for their development. But are high in the height category.
We eat healthy too. Hardly any junk.
Our Pediatrician has no problems, with they frequency of their eating or appetites.
My daughter, who is now 9, eats a lot. By a lot, I mean, she gets hungry very often. So we let her eat. The reason is: BOTH my kids, know their body and its cues. They KNOW when they are hungry or full. When full, they stop eating. When hungry, they know it and tell me.
They do not eat out of boredom or for emotional reasons. They eat, because they are HUNGRY.
AND when my daughter is going through a growth spurt, she can get hungry even 20 minutes after eating a meal. AND she is the type, that needs to "graze" otherwise she gets fussy.
She has been this way, ever since she was born.
With my son, who is 5.... he too will eat frequently, when having a growth spurt. He is a picky eater, but eats well. PER his body's cues. BUT... my son is a "grazer." Meaning, he will eat small amounts, throughout the entire day. That is how he always has been. My Husband is a grazer too. Even if they do eat their meals at meal time. They are grazers. Many people are this way. It is actually, a healthier "way" of eating.
When my son or Husband graze, they are not eating, "meal" sized things. But small quantities, until they are full. Which does not take a lot. They know, their bodies. And that is a good thing.
Eating a "lot" does not mean, the person is eating a "lot." It means... that the "FREQUENCY" of their eating... is more frequent. Not that they are pigging-out, each time. So there is a big difference, between eating a "lot" and the frequency of it and the actual "amount" they are eating.
As I said, my kids eat FREQUENTLY. Which is common for kids. They are very active and their metabolisms, are higher. Thus, they need to graze. And need to have more than ONLY 3 meals a day. Kids, need to "snack." Snacking does not, mean it is "bad." It means, that they CAN have things in between meals.... and just feed your kid healthy things. Not junk food.
And to eat by their body's cues, for hunger and fulness.
Your child, as you said, is LEAN. He is not overweight. So you do not have to be concerned.
My kids are lean. They eat very frequently. I am feeding them ALL day. But it is fine, no big deal, and they are healthy. Because I do not feed them junk. For my son, a "snack" can even mean a little salad. Which he loves. For my daughter, she eats fruit. So you see, "eating" frequently, does not immediately mean it is "bad."
If my kids are HUNGRY and their body needs it, I feed them. And my kids are active. As most kids are.
The key thing is: that a child or person.... KNOWS their body's CUES... for hunger or fulness. We have never "made" our kids, eat EVERYTHING on their plates or forced them to eat etc. For example. We taught them to eat according to what their body is saying. Full or hungry. If they get full after even just 4 bites of something at mealtime, fine. They are done. In that way, a child/person, learns to eat, for normal reasons. Not dysfunctional reasons. And then, they learn to eat, for their body's cues.
My daughter, eats frequently throughout the day. Because she is hungry. And she has always been that way... ever since she was a baby.
One summer, she was eating like every 1/2 hour or less. She was HUNGRY. And then, once school started, she grew in height a TON.
As I said, our Pediatrician, has no problem with my kids' eating habits. In fact, he said they are eating properly. They eat per their body's cues, and know it, and they are lean TALL kids who grow like weeds. And they are eating, healthily. Not junk.
We taught our kids, about nutrition.
I NEVER fear, that my kids are eating for the wrong reasons. Because, they KNOW their body and its cues for hunger and fulness. They never, eat, just to eat. They eat, because they are hungry.