7 month old pulling up to stand

An

My son will be 7 months on the 16th and he just started crawling last week. He’s been trying for a whole month and just mastered it. Now as if I didn’t have enough to worry about he’s been pulling himself up on furniture and his crib which is why he’s in the play pen but he obviously learned how to do it in the play pen too. Isn’t it too early for him to do this? I thought I would expect this around 9 months not 7.