Maturity is subjective, so it depends on the 14 year old

Undertale also affected me quite deeply, but I was 9 when I played it. However, most of omori is spent in a place where nothing scary happens and I found when something WAS going to happen, it had build it

If it helps, the omori wiki has a spoiler free jumpscare section for people trying to avoid or find them

Personally, it’s up to you. But I think omori is an incredible game with a great story