Hello Lynne
I did the America's Golden West tour as my first JY trip last summer (was 33 at the time). Age really isn't an issue. The tour itself is fantastic, my tips on the excursions:
San Fran - I had always wanted to go to Alcatraz and even pre booked on the internet but didn't end up going. You get really up close to it on the bay harbour boat trip and there were so many other things I wanted to do such as ride the cable car etc. In reality you will only have 1/2 a day free (actually, more like 4 hours!)
LA - like Mick, Universal Studios was an included excursion for us but I would still recommend going, albeit we were there in the school summer holidays so did a lot of queuing. The LA tour in the morning is great.
Palm Springs - I did the tour in the morning (desert zoo was good, driving around looking at where people you have hardly heard of once lived not so much - I fell asleep). When they say hollywood houses they mean hollywood stars of the 50's & 60's. Didn't do the Aeriel Tramway as by that stage I was ready for an afternoon off! With hindsight I would probably swap that day and do the afternoon tour, its about the only chance to have an extra hours sleep in the morning.
Las Vegas - didn't do the Rat Pack show as not my taste in music, but there are plenty of other shows which the hotel concierge can sort tickets for you. There are also lots of free 15 minute 'shows' in the various hotels, and don't miss the fountains at the Bellagio - we went back again on our last night!
Grand Canyon - I did the skywalk trip which was fantastic and gave plenty of time to just sit and take in the breathtaking scenery. Whilst the people on our trip enjoyed the helicopter 3 in 1, they did say it all felt a bit rushed.
My top tip is to go with what you want to do, excursions are personal preference and you will have such a great time whatever - don't miss the opportunity!
Have fun
Caroline