Rock, as a senior in high school (17 years old and 35 years ago) I wrestled at 138 pounds. Before the season began I weighed 150. I was skinny! (This is the first time in 20 years I have been below 200 pounds.)
When you are older it is so easy to add weight. I know your Dad is pretty slender too. Perhaps you will be slender your whole life. Just count it as a blessing. There are so many health problems associated with weight. Perhaps you will avoid them.
Add muscle if the weight doesn't come so what. I have known many young men that were very strong but didn't have a lot of weight.