Mature sweet male lead

Someone who isn't petty and obnoxious, or rude.  Getting kinda sick of those.  Maybe like the guy from Boss and Me or Love O2O.  Protective guys are a plus.  

Naked Fireman
Doctors 
Goodbye Mr. Black (but I wouldnt recommend the show) 
On The Way To The Airport
Prince of Wolf (not the most mature, he's a man with child like innocence) 
Sweet Stranger and Me 
The K2 
W 
Will You Be There? 
Evil Minds 
Falling For Do Jeon 
My Love Eun Dong 
The Eccentric Daughter-in-Law 
Angel Eyes

I tried to find those that were mature and sweet from the very beginning of the show, not sure if these would fulfil your criteria :) 

Aww I also search character like Xiao Nai in Love O2O ahaha

But in my opinion:
The K2
Playfull Kiss
49 Days
Good Morning Call (Recommended)
Just You
She Was Pretty
You Who Came From the Star

if you have the patience to watch longer dramas then I suggest 
Five Children - 1st male lead never gets angry or petty, 2nd male lead is full of himself in the beginning(he's famous golf player in it) but you'll see a 180 turn around when he embarrasses himself. 3rd one gets angry only once, 4........., 
i liked the 2nd couple better(Sung Hoon+Shin Hye Sun)

Buzzer Beat
Doctors
Kingyo Club