Motorcycle Safety & Driveability: What size 1st dirt bike for 53 115lb 13 yr old boy, dirt bike, bike shops

Question
see subject line

Answer
Hello Walt

It's going to depend on a lot of things.  Everyone is different.

Has he ridden before?  If not, does he have similar  experience - mountain bike, BMX, etc?  

Has he, or will he, attend a reputable Riding School?

Regarding the engine output, a lot of that will depend on the above questions.  

Regarding the frame and type of bike,  I would recommend that you to take him around to various bike shops in your area and try a few.

Cheers