There are a lot of students in my original year 12 year (2008) at my school who are doing pathways. I'm also doing pathways, although I don't consider it as such. I left during my first HSC year (08) and took 7 months off due to health reasons, term four last year I returned to the same school to complete all 5 subjects in the one year.
Everyone from my original year fit in great with our year twelve now. We were all really accepted right from the start - it does get frustrating at times being 19 around a bunch of younger kids, some of which are only just turning 17 and there are definitely times when the age gap feels huge, but the social side really isn't that big a deal. Yes, its hard being seperated from your friends, especially when they are off having adventures overseas or at uni, but you see them outside of school. If anything, my social life has grown substantially - I have double the amount of friends I use to have.
Ultimately though, its a personal choice. Because I'm doing all 5 subjects this year, and I'm constantly busy, I guess I don't notice the gap that much. But my friend who only has 2 subjects this year, does at times. Make sure you have a good parttime job during the second year of your pathways.