Back into biking in my 40s, I started with a Giant NRS 1, which had just won 2000 Best Bike and got 2001 Overall Bike of the Year. Here's the review http://www.mtbr.com/cat/bikes/bike-full/giant/2001-xtc-nrs-1/prd_355650_95crx.aspx
Just a mid range bike but with excellent specs and at the time superior design for locking out pedal bob while keeping suspension engaged. I think it was the first auto lockout utilizing geometry instead of some mechanics like a pin. Loved it then and still ride it now. In fact one of the reasons I selected my new location was because of all the bike trails nearby. Just minutes away I've got about 30 miles of off road, mostly shaded for summers.
I first got into mtn biking at Oleta in Miami on a rental after seeing how much fun it looked. The bike sucked but I had this smile on my face the entire time and was hooked that first day. Researched bikes right away, got some skills going, only did two endovers including one that threw me about 15 feet, not real smart in your 40s with just a helmet & gloves.
If you are going to get into technical trails, get yourself some protective gear. After that last fall I started dressing like Darth Vader. Now I just do the less technical rides. So I got to enjoy about 10 years of the really fun stuff. Wish I'd known about mountain biking sooner.
Then I started riding road on the mtn but couldn't get up enough speed to make that satisfying so I got a roadie now too. They're very different rides.
In your area some of the fun trails are Oleta as well as Markham out by Weston. Also ride the berms out in the Everglades, you'll find various access points. On a hot day you can do Quiet Waters up in Deerfield, not a lot of trail but it is all shaded. I wouldn't do a hardtail there on the medium or tech trails, full suspension only as there's a ton of Australian Pine roots. Hard tail can do their easy trail though. A lot of the Everglades you can do with just a hybrid, not even front suspension required on the double tracks. It's a beautiful ride out there but just do that in winter as there's often no trees and summer would burn ya.
A real nice stretch of Everglades is Parkland to Boynton, out in Loxahatchee. Another nice ride is Jonathan Dickinson up in Jupiter. Most of the parks have easy, medium and tech trails. If you get very adventurous, you can ride on top the dyke around Lake O on a hard packed double track. That's also a winter event as there are no trees up there and few places to stock up so bring lots of water and some snacks. Or just do like the Belle Glade to Pahokee stretch, maybe just 12 miles plus the trip back.
Here's Lox just north of Parkland. It's gorgeous out there.