Do you want to feel bad? Ask TikTok how old you look.

Cherri Gervais got her first gray hair as a teenager.

“It’s genetic,” she said.

Her hair color, a striking shade of silver, is the first thing people on TikTok noticed when she asked them to tell her how old she looked in a recent video.

The guesses varied enormously. Many were right, or close enough, Ms. Gervais said. (She turned 34 this month.) Others suggested she was in her 60s or 70s.

Ms. Gervais, who lives in Kansas and works for a part-time beauty company, said she decided to post her video after coming across similar TikToks.

“I saw someone from Gen Z doing it because they said Gen Z is aging faster,” she said, referencing a recent online theory that teens and young adults are aging faster and more visibly than their millennial counterparts.

Her video is part of a trend where users, mostly women, ask strangers to comment on their appearance. Ms Gervais said many of the responses she had received were unkind.

“People told me I should dye my hair, get eyelashes done and get my eyebrows done,” she said. Several suggested she looked like a “middle-aged mother.” “There’s nothing wrong with that,” Ms. Gervais added. “But I’m not a mother.”

Jalisa Silva-Toney, a 21-year-old social work student living in Point Pleasant, W.Va. lives, also participated. “I was just curious,” she said, noting that people often misinterpret her age.

Part of the reason she wanted to post her video, she said, was that she hadn’t seen many other black women participating. She added that TikTok’s culture of constant comparison could fuel the trend and larger debate about her generation’s frown lines and skin elasticity.

Pri Maha, a business analyst in Atlanta, said she asked people to guess her age in a recent TikTok video mainly out of curiosity.

“I do see content from big influencers who are only 23 and getting Botox,” said Ms. Maha, 27. “Sometimes I think, ‘Oh, should I do that now that I’m older?’”

She added, “I feel like there’s definitely a push where I see younger girls doing work, or just trying to look as young as possible while they’re still super young.”

However, not everyone participated just out of curiosity.

“I have pretty thick skin, and there aren’t many things that hurt my feelings,” says Morgan Driscoll, who works in communications at a technology company and lives in Weymouth, Massachusetts. “I knew it was worth posting because of the opinions.”

As someone who aspires to have a large number of TikTok followers, Ms. Driscoll, 30, saw joining the trend as something of a business opportunity.

“I didn’t post it because I was looking for validation,” she said. “I posted it because I knew it would get engagement.”

She was right: her video has been viewed more than 100,000 times.

Most of the comments were about her eyebrows. “I have millennial eyebrows,” Ms. Driscoll said, meaning her eyebrows are thin. She would “fix” them this week, she added, based on the TikTok feedback.

“I think the worst thing I got was a comment saying my neck is getting shot, which is insane,” she added. “I mean, I just turned 30!”

But for many TikTokers, any engagement is good engagement.

“A comment is a comment,” Ms. Driscoll said. “I don’t care if they’re trolls. I don’t care if they tell me I look like a toad. I just want the reactions.”