My dd is 2 1/2, 40", but she has a really long torso. I noticed today that her head is almost of the top of her Decathlon. What are the limits for this seat? I bought it less than 6 mos ago! I assumed it would be fine till she was at least 4 since most people say their kids can ride in the Marathon till 5 or 6. What seat do you get after the DC/MA? I want her in a harness seat as long as possible.