He's thirty at the very most - he looks very young.
Tips
usage
至多 sets an upper limit: 'at most'. Mirror it with 至少 (zhìshǎo, at least) which sets a lower limit. In writing 至多 is preferred over the colloquial 最多 for a slightly more formal feel; both are interchangeable in most contexts.
memory
至 = 'to the extent of / reaching' + 多 = 'many'. Reaching the most = at most.
