= Solution
Normalize the present <scale factor> to $a(t_0)=1$. In a flat universe containing <radiation in cosmology>, <pressureless matter>, and a <cosmological constant>, the <Friedmann equation> is
$$
H(a)=H_0\sqrt{\Omega_{r,0}a^{-4}+\Omega_{m,0}a^{-3}+\Omega_{\Lambda,0}},
$$
where $\Omega_{r,0}+\Omega_{m,0}+\Omega_{\Lambda,0}=1$. Since $dt=da/(aH)$, the <age of an FLRW universe> is
$$
\boxed{t_0=\frac1{H_0}\int_0^1
\frac{da}{a\sqrt{\Omega_{r,0}a^{-4}+\Omega_{m,0}a^{-3}+\Omega_{\Lambda,0}}}}.
$$
For a matter-only flat <Einstein-de Sitter universe>,
$$
\boxed{t_0=\frac{2}{3H_0}}.
$$
Taking the present value $H_0\simeq70\ {\rm km\,s^{-1}\,Mpc^{-1}}$, for which the <Hubble time> is $H_0^{-1}\simeq14.0\ {\rm Gyr}$, gives
$$
\boxed{t_0\simeq9.3\ {\rm Gyr}}.
$$
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