i see alot of older blokes at my gym that go quite often aswell, and who dont seem to make a lot of gains, the things i notice about these blokes is there doesnt seem to be any structure in their routines and they dont seem to fully understand the excersise they are doing and thus have very poor form.
Maybe going back to the basics might be a good option for you, and incorporate your 3 main compound excercise, benchpress, squats, and deadlifts.
If you were to go to the gym 3 days a week, then maybe you could structure your workout like this.
DAY 1 (monday)
3-4 sets of 10 barbell squats (if you have any back issues you may choose to use a hack squat machine, but it is definately best to do it with barbell)
3-4 sets of leg extensions
3-4 sets of calf raises
3-4 sets of leg curls
DAY 2 (wednesday)
3-4 sets of flat barbell benchpress
3-4 sets on peckdeck
3-4 sets of shoulder presses
3-4 sets of upright rows
Day 3 (friday)
3-4 sets of deadlifts (you prolly need professional guidance on acheive coorect form for this lift)
3-4 sets of seated row machine
3-4 sets of lat pulldowns
3- 4 sets bicep curls
3-4 sets of tricep extensions
Dont be afriad to ask someone that works at the gym for a demo on proper technique, i think nailing the technique on these simple excersises alone will give you some good gains and when you have mastered them you can start changing up your workout from there.
Nutrition is just as important as the workout itself to make good gains, a good protein powder should be consumed 45 mins before your workout and within 30 mins after, and then a good high protein meal within an hour.
You should be consuming about 250gms of protein a day, mainly from whole foods such as meats.
http://www.proteindirect.com.au/products.html
the WPC is all you will need.
once you do master these excercises dont be afraid to push yourself and ask for a spotter if neccessary, some times that extra 5kg plate your scared to put on is not that scary once you start lifting it.
i hope this helps, and addresses the issues you have.