I agree with the others, it's more ability based than age IMO. Â My girl has been doing "toddler" things since 9ish months. Â That's when she started walking, and her vocabulary exploded. Â She's 11 days away from her first birthday and speaks in (short) sentences. "It's good" "I love you" "I did it!" ect. Â
Â
I also think it has to do with their "look" My cousin has a baby a month younger than Lila, but he's bald as can be so that makes him look more babyish than my girl who has always had a head full of hair.  He's also a big ol chunk of baby! He's got the most adorable baby rolls, and my girl has always been bitti.  He outweighs her by 3 or 4lb, and so does  my nephew is 3mo younger he's also a big baby. Â
Â
I think toddler is when you start seeing them as little people vs babies. Â
Â
Baby Lila ( End of May)

Â
Toddler Lila (end of June)

Â
Those pictures were taken a month apart (to the day!) but she's babyish (imo) in the first one and definitely toddler in the second. Â
Â
Current Lila (end of August)

Â
Maybe my girl is a bad example.. she's always kinda been a little person!Â
Â
Â