From a bit of clicking around, its linked no-where but the footer, so if you're making an account they don't tell you to read it. Easy to miss.

Quoth Article 8:

1. Where point (a) of Article 6(1) applies, in relation to the offer of information society services directly to a child, the processing of the personal data of a child shall be lawful where the child is at least 16 years old.
   Where the child is below the age of 16 years, such processing shall be lawful only if and to the extent that consent is given or authorised by the holder of parental responsibility over the child.
   Member States may provide by law for a lower age for those purposes provided that such lower age is not below 13 years.
2. The controller shall make reasonable efforts to verify in such cases that consent is given or authorised by the holder of parental responsibility over the child, taking into consideration available technology.
3. Paragraph 1 shall not affect the general contract law of Member States such as the rules on the validity, formation or effect of a contract in relation to a child.

The referenced point (a) is in the conditions for data processing to be lawful:

the data subject has given consent to the processing of his or her personal data for one or more specific purposes;

In essence: The age of consent is 16 when it comes to your personal data. A completely different question is whether lemm.ee even processes personal data, even more so in a matter that requires consent. Because unless you doxx yourself lemm.ee knows nothing more about you than your IP and, presuming best practices, only keeps limited logs around for strictly technical purposes which don't need consent. That point (a) is only one condition under which personal data can be processed, there's also b, c, d, e, and f.

...not that I'm saying that the legal notice is bad it's good. It's overzealous and overcautious going beyond the letter of the law and event intent, reaching into the fabled realms of actually giving a fuck. Like, if the law says "assault is bad" then this notice is saying "please all cuddle, ok?"