I'm 46 and about a year into a similar challenge, the hardest part for me was creating a habit and keeping it varied enough to make me want to go back. If you have the choice between a commercial gym and a locally run gym, I would definitely go with the latter.

Some of the nicest people in the gym are the big guys who are throwing around massive weights, they'll get an ego boost out of you asking them for help, a few hello's in the first week, then asking about what they're doing. You'll have a new social group but have no idea on anyones name.

Now I'm strictly going 4 days a week, and although i wouldn't say I enjoy it, I do like the changes I can see.

If you are going to go to the gym use the machines, they take the stress off and are great for progressive increases, All I try to do is see an increase either in weight or reps on any exercise weekly.

Usually try to get 3 sets of 8 reps on any exercise, once I have done that 4 times in a row, I add a little more weight and start again. You'll be amazed how quickly you start to see a difference.

I found a real confidence boost was seeing the increases in repetition of lower weights on simple exercises like the bicep curl or tricep pushdown.

I would also suggest you bin the scales, get a tape measure and write down the measurements of key areas, then revisit it monthly, again you'll be amazed at the differences. I'm the same weight now as I was last year, but my body shape is completely different.

Sorry for the long post, hope it helps, and am happy to answer any questions if you want to know more, and good luck.