"Seventeen? I think... I'm not sure. I was fifteen when I met my boss, and then we had what felt like a year of peace where the family was being established... and then, traveling ten years into the future, and the two worlds I was in before this one. I'm sure I'm somewhere around seventeen years old, now."

Plus with the first world being so focused on something he's sure he wasn't too ready for (not even having given away his first kiss and then being on a sex-crazy planet), it's been like his maturity has been thrust on him forcefully. He needs more opportunity to live with and embrace some of his more childlike innocence.