10 rp worth of mystery gifts says Ekko is older than he looks.

Maybe chrono-displasia, just a theory.

With the ability to rewind yourself back to a specific point in time, I wouldn't be surprised. His time technology affects himself more than his surroundings, or perhaps more so his immediate surroundings.

Probably same sickness Zilean has, but this time forced by someone outside him.

Doubtful, you can see in his teaser video that he doesn't rewind himself, retaining any damage that he took previously.

but he cant be, age is based on time pased so if hes 16, goes back a year, hell be 15 with the body and experience of someone who was 16 etc. his time is just diferent than normal time.

like say if he was born in 1990, no matter how many times hes rewined, he would be 25 years old because time is a man-invented concept. and 1990-2015 is 25 years.

Seems rather likely. Unless VIs lore gets changed,she grew joined a gang in Piltover when she was 6,so she most likely came to Piltover when she was 5 or 6 years old.

If Ekko knows Vi,then he'd need to be around the same age(because if he was any younger,then he'd likely wouldn't remember),so it is possible that the time travels stopped/slowed down his age progress.

Another possibility is that he traveled through time quite a bit already and that the age difference is a product of that.

I bet you, Ekko is ziliean in his youths time, when he could be swift as a coursing river!.... before he became so crippled that he needed a skill to speed himself up

Several people have mentioned chrono-displasia, but Ekko can't have Zilean's disease. Chrono-displasia is an actual inability to experience the present, instead experiencing the past and present in some mishmash of time displacement. Ekko is far too present in reality to be spaced and stretched out across all of time.

Doctors hate him. People want to know his secret.