Welcome

Started  at 58 myself and still at it at 61, but played in my early twenties for a bit.  Many other late learners  here so you'll do fine. 

As for recommendations on an acoustic both of those models should serve you well. I have a Gibson l-00 which is smaller than the j45 and I love it so partial to them, but would never discount a Martin or a Taylor. Whatever feels more comfortable to you. Good luck. 

Moe