My therapists have always been a bit older than me (well, my first was quite a bit older but I was still in college). I wouldn't want a therapist younger than myself - not by much anyway. I'm nearing retirement age, with grown kids and a dying parent. I would need a therapist who at least has a similar life experience (as in a bit later in life, past the parenting toddlers age, etc.) My last two therapists have been just slightly older than me, both family people with kids and spouses, etc. A 30-something without that kind of life experience just wouldn't have that much to offer me as far as some confidence that they have any real-life understanding of what it is to be at this stage in my life.

That might not matter in the least to someone else, but for me, stage of life makes a difference. Just like someone quite young might feel more related to by a bit younger therapist perhaps.