See if you can figure out how he's getting out. When my first son first climbed out, he was really proud of himself and showed us how he did it when we asked. He just climbed over the side very carefully. He was older, and could have gone to a big boy bed, but we talked to him about not climbing out, and it worked. He stayed in and called for us instead. But that's his personality.
My second son was older when he started climbing out, too. We had to spy on him to see how he was getting out, and it turned out he was using other furniture! He could climb out onto an extra deep window sill, then down onto his dresser, then jump down to the floor. After a quick rearranging of the room, he couldn't do that anymore and stayed in for a few more months.
17 months is quite early to be in a big boy bed, IMO, especially for a boy. They're just not as mature. And we tried doing it at 18 mos. for my oldest son so he'd be out of the crib when his baby brother came, but it was a disaster! He'd wake up in the night and get out of bed just because he could. Then he'd sob because he was so tired and groggy. After 8 days of that, I got the screw driver at 3 am and put that stinking side back on the crib! I bought another used crib for $50 and it was worth every penny because we were all happier.