His perspective is completely distorted because he was an older guy before he reincarnated so he still thinks of himself as older. That's why he keeps calling the hero a lolicon even though the hero and the girls are all the same age, and he sees no problem with wanting the mamas because as far as he's concerned, he's the same age as them.
Now as to why he sees the girls as kids but not the hero, I don't know.
To MC, the only Female worth any attraction are Mama's. Anyone younger or non-Mama Females are all underage to him (I am sure he even considers 20 years olds as underage).
Basically MC's pov is quite narrow, as he only applies this standard to females, and not on males like the Protagonist.
To him, every Male should only be interested in Mama's, and should stay away from younger or non-Mama Females
Anyone not interested in Mama's is a "Lolicon", even if they are of the same age.
Aka., for MC
- Lolicon Males ❌
- Shotacon Mama's ✅