Marner turns 18 in May and currently has:
41G 69A for 110P in 53GP (2.08 PPG)
The season in which Hodgson turned 18 (in February), he had:
40G 45A for 85P in 68GP (1.25 PPG)
Even the next season (and a year makes a big difference in juniors), Cody had:
43G 49A for 92P in 53GP (1.74 PPG)
Interestingly, when Stamkos turned 18 (in February), he had:
58G 47A for 105P in 61GP (1.72 PPG)
Also, Tavares turned 18 much earlier (September) in his draft year, but still only put up:
58G 46A for 104P in 56GP (1.86 PPG)
Though, clearly both were drafted more as goal scorers than Marner would be.
Some others:
Taylor Hall: 40G 66A for 106P in 57GP (1.86 PPG)
Tyler Seguin: 48G 58P for 106P in 63GP (1.68 PPG)
RHN (in WHL): 31G 75A for 106P in 69GP (1.54 PPG)
Yakupov: 31G 38A for 69P in 42GP (1.64 PPG)