He is 10 and he kinda throws like mike miller/belmo. two fingers in the hole and two handed. also, he takes 2 or 3 steps 

I want him to be traditional stroker type, but he seems comfortable the way he throws. Should I let him be and wait till he gets better? he bowled since he was three years old but not often and always two handed. And as he got older, he was finding ways to bowl. He doesn't want bumpers anymore and want to use the 14lbs balls I haven't sold.

what do I do?

he has a misfit and a slingshot to start.

I would let him do whatever he wants to. Just keep him interested in the sport (oops I used the "S" word). 

After a while, I would think about trying to teach him to throw at least at his spares with a one handed style. This way he may adapt into being able to have both styles at his disposal when he gets older.

If you feel it is worth it, hire a good coach and get him some lessons. Many youth programs have coaches - some good, some horrible.

At his age, IMO, the best thing you can do is let him have fun.  When he's ready to get serious about improving he'll let you know.  --  JohnP

I read a recommendation in bowlers journal or similar publication that said have them bowl with a ball weight that matches their age.  So 10# at 10-years-old.

Encourage him to join the league so he makes friends in bowling.  Let him have fun. 

I'd be careful about him using 14 lbs. though.  Two handed is fine, but with a 14 lb ball he'll likely throw it too slow for whatever rev rate he has, making any reactive ball hard to control, which may lead to frustration rather than enjoyment.

Side note: If he loves bowling, and you love bowling you'll have that common ground when he's 14-18 years old and the "rational" part of his brain is dormant, and he'll listen to any voice as long as it doesn't belong to Mom or Dad. 

My son (now 30) and I could ALWAYS go bowling during those difficult teenage years, no matter how stupid he acted, and we could bowl, talk about school, life, friends, you name it...  You may not have the chance to have those conversations within the walls of your home because he'll see it as "Dad lecturing" and will probably tune you out until he's a little older.

We're now the best of friends, and he's anchor on my team.  I cannot imagine a father and son any closer.  Looking back, bowling was very important, and I'm certain, kept both of us out of some trouble.

Best of luck to you and your son.  Enjoy whatever you can together now to lay a strong foundation for your relationship.  Most teens experience some difficulties in life regardless of how great their parents are.  If you're close hopefully he'll come to you with his issues instead of the 10,000 other "voices" that will pull him in any other direction.

Agreed...

I will try this season if he would like to join the youth league here. It'll be a good way too to make new friends in bowling...

(His swimming is over and he could use some other activities where I don't get sun burnt and pack up like I'm going camping once or twice a month, eating all those bbq's and chips while his coaches wave their fingers at me...lol)

Hey OP.. what is your 10 year old's bowling average about?

I only ask, because I had a bowling ball shipped to my office. I was showing people my new Seismic Equalizer and the Indian guy comes over and says his nephew is youth state champion.. I wasn't sure if he was just saying that or what, so I went to ball.com and see his average is 58. I might have chuckled, but honestly I don't know if that is good or bad for a 10 year old. I was expecting the score of a state champion to be higher.