I've had five babies, all born at home.
#1 (10 lbs, 4 oz)- 23 yrs old, 7 hour labor which I would describe as strong but easier than I expected and pain free, tore, challenging recovery with baby in the NICU
#2 (8 lbs, 10 oz)- 25 yrs old, 6 hour labor with contractions that were more challenging for me than my first, I passed out afterwards so laid low postpartum
#3 (9 lbs, 7 oz)- 28 yrs old, 1 1/2 hour labor that was crazy strong (labor started right in second stage), easy recovery
#4 (10 lbs, 11 oz)- 31 yrs old, 40 hour labor due to baby's position and size, tore, challenging postpartum with pelvic pain/pubic bone separation
#5 (10 lbs, 8 oz)- 34 years old, 3 hour labor after a couple days of early labor contractions on and off (prodromal), strong and fluid, felt fabulous afterwards and had easy and quick recovery
I'm not pregnant with #6 and I'm almost 38 yrs old. This pregnancy has been my easiest, and I'm hopeful that the birth will be great too!
I don't think it's so much dependent on baby's size or your age, but I do think the baby's position has a lot to do with how labor progresses. That said, my last baby was OP most of the time preceding labor and I was worried he was going to engage that way when labor began and would be born posterior, but turned at some point in labor so that he was not born OP.
Also, my labors that were easier started with my waters breaking, so baby's hard head was on my cervix which I believe made my contractions more effective and labor more efficient. My two more challenging labors, where I felt stuck or less strong or whatnot- my waters didn't break with those until just before I pushed them out.