Firstly, I am sharing a card that I cased from Heather Klump, this card is suitable for boys of all ages, just by changing the number.
Below is a pocket card is the perfect card to use if you are wanting to give a gift voucher for the gift. You could also fold some money in half and stick that in the pocket instead of a gift voucher. I have made many of these cards over the years and they are very suitable for teenagers, and you can change the colours to suit a female or even make a Christmas version.
Lastly, a very easy grunge looking birthday card perfect for a young teenage boy. The stamp sets used were: simply stars, gorgeous grunge and sassy salutations for the sentiment.