From Lugo onwards, the Primitivo is the Primitivo in name only: relatively flat, through a fairly densly inhabited area until Melide, and then mayhem after joining with the Frances. Physical challenge is nothing out of the ordinary, compares to Sarria to Santiago or Tui to Santiago on the Portuguese. Easy peasy. No, it is not "one of the most difficult caminos", no you don't need to find a "more widely travelled route and less difficult". I. Fact you would be hard pressed to find easier and when ot comes to more travelled as well, especially after hitting Melide. Really.
You will meet lots of people your age, as well as younger and older ones.
As for " specific problems", can you give us an idea of what you have in mind so we can answer your questio with more precisions? I cannot think aboit anything particular about this stretch I would caution anyone against. No long stretches withough food or water, no huge climbs or descents one could tumble down.
The only part where I scratched my head was leaving Lugo. Ypu cross the plaza, walk by the cathedral, walk out of the walls. At the river, after crossing, signa were iffy when I walked. It was not clear if you had to walk straight and up, wchich I did, or follow the river to your right, which others did. Turns out both come together later, so nothing to worry about. Also, as I was leaving on a Sunday all bars (which arw not discos but coffee and eating places) were closed in the morning, should have picked up some thing to eat for breafast the evening before.
The Cathedral in Lugo is very important to catholics and there are ladies there who volunteer to give people a tour of the cathedral. Well worth it, and a beautiful stamp for your credencial at the start of your camino. This cathedral is important because it is one of the very few (3-4?) churches in the world allowed to display the host on a continuius basis, and it has done so for hundrds of years. On of its side chaples is also by the same man who designed the current Santiago cathedral facade.
The muni albergue down town is very large, so you will meet many people. If you are unsure on day one, want someone to walk with you out of town, lots of people you can ask for company.
These were my etapas after Lugo:
1- Lugo to San Roman: 20km. Stayed at O Candido, a wonderful "helpt yourself to anything in the fridge, we'll settle the bill later" albergue.
2- To As Seixa: 14km. A lovely old stone barn restored by a young local architect. Good restaurant 200 meters away for dinner.
3- To Melide: 14.5km. A shock for me, as kt is with so many coming from days of walking a quiet Camino. Packed with people with backpacks. Do no miss visiting the tiny church of Santa Maria (I think), on your right along the Camino as you leave town. Ask for a tour and explanation of its decorations. It is a gem.
4+: follow the heard into Santiago.
This is a website I like to use:
http://caminodesantiago.consumer.es/mobile/los-caminos-de-santiago/primitivo/