Age group dilemma in surveys

So I'm new to research and I started a survey to understand users a bit more. After doing a HotJar Poll/ Email Survey on one of the sites I'm managing I'm getting 55+ as an age group for the majority of users who responded. Both Google Analytics & Alexa Pro are reporting the majority of users in the 18-24 range. What can be done usually about that?

Also if some of the respondents skipped some questions. Do I disqualify them?

Thanks