Boyishly

2 clues
How young guys behave
In the manner of a lad
Similar answers:
Apishly
Bearishly
Beatharshly
Boyin
Boyish
Boyishly
Brashly
Childishly
Dealharshlywith
Doltishly
Eatfreshly
Feverishly
Fiendishly
Fleshly
Freshly
Freshlybrewed
Freshlymodlawn
Garishly
Girlishly
Harshly