It can still work, but not as a standalone idea anymore. A single age calculator won’t really do much unless you somehow bring something different to the table. The competition is too old and established in that space.
Where I’ve seen better results is when people turn it into a broader “utility” site instead of relying on one tool. For example, combining age calculator with related tools like date difference, work experience, retirement, etc. and targeting long-tail queries around them.
Also, a lot depends on how you plan to get traffic. Pure SEO is harder now unless you go after less competitive keywords or build topical relevance around time/date calculations.
So yeah, profitable? Possible. Easy? Not really. It’s more of a volume + strategy game now rather than just launching a single tool and waiting for traffic.