Try "Have Spacesuit Will Travel"
"Pokadyn of Mars"
"The Rolling Stones"
"The Star Beast"
"Stranger in a Strange Land" may be a bit too early for someone that young as are much of his later works
I think "The Moon is a Harsh Mistress" works, in that category.
Would you believe I actually got all 4 of the ones you names plus Starship Troopers a replacement of my Citizen fo the Galaxy and 5 more adult Heinlein's for me to keep on ebay for $2.50 + reasonable shipping!!! It had to be God!!! Total for all 11 old paperbacks was $5.50!!! Heck, you just can't beat that!!!