DS is four years old and I am *finally* feeling like I have a semblance of a life. I do work full time hours lately, but not 9-5. For us, they key is BEDTIME! He goes down at 7pm and wakes up at 6am. The key to my sanity is a pretty rigid schedule: dinner, put DS to bed, work out, respond to messages and set up social activities, then spend about 3 hours on school. I wake up at 4:30 am and exercise. Really, school takes up 99% of my free time, but I make the most of that 1%. I spend my free time cultivating friendships, stealing DH away for a quick overnight somewhere, etc. I don't consider cooking, reading, or gardening as hobbies, since those are things DS and I do together, so it's more like our special time together.
Early Saturday mornings are reserved for dates with friends (pedicures, running together, etc.). I love making time for my friendships and feel like it's time well spent.
No matter what, once a week I take three hours away from schoolwork, working out, etc. to focus on learning something new. Right now I'm taking a pottery class once a week. Last spring it was glassblowing. When the potter wheel class is over, I'll move to printmaking. I've been doing this for a year now and have tons of incredibly useless skills but lots of new acquaintances and a greater sense of self-fulfillment. My shelves are littered with things like lopsided bowls and deflated glass orbs.
If you have younger children and are feeling lost, just give it time. They are less demanding as they get older and you'll eventually find time for yourself. Let go of your guilt about not spending every moment with your kids- you need time for yourself, too!