If someone is young, but very overweight, it can make them look much older. Teenagers generally have a very small frame, and by 25 we look more filled out. If a teen is heave it can age them ten years. It works the opposite direction too. A 25 year old who is very thin can look like a teenager. So, if someone is very heavy I really study their face if I’m trying to guess their age, instead of first impression.
Past age 30 there are different cues. Like lines on the neck is a give away in my generation for over age 40. My mom always told me to protect my neck from the sun, and I didn’t listen! I regret not listening to my mom.
It still can be really hard to determine someone’s age. Especially, people with darker skin tend to “age” less. My husband (olive skin) could pass for 20 years younger than he is. In his 50’s he still has thick black curly hair and barely a wrinkle.