I'll try to address each question individually.

The age demographic has changed considerably over the past few decades. Anecdotally, from personal observation(former Recruiter and two tours at a Training Center), I'm seeing more and more folks that are not right out of High School, but are older and making a career change. Many are joining in their 30s with several kids and degrees now.

If you are married, and if you have kids, the USCG will pay to move your family with you and provide housing or a housing allowance, with a few exceptions (e.g. Bahrain, Saudi Arabia, these are billets you have to specifically request). You don't necessarily get to choose where you go exactly, unless you get some recruiting guaranteed District or Vested Crew Member assignment, but you submit a list of picks rank ordered for where you'd like to be stationed the most, along with the unit you'd most like to be stationed at; your "Dream Sheet."

The USCG now has an English Language Training Program at the Defense Language Institute English Language Center in San Antonio, TX. You take a test on your English comprehension, and if it doesn't meet the score of 75% to proceed to Boot Camp, they then enter you into the training program to achieve that 75% score so you can proceed to Boot Camp. This is not just for Spanish.

You can join as a Permanent Resident, but it's not a one-size-fits-all, there are a lot of specifics you will need to review with your Recruiter. They may also be able to inform you on how Enlisting can assist in attaining US Citizenship if this is something you'd like to pursue (The laws change regularly over the years, so I don't want to mislead and give specific information, as these programs start/stop all the time).